diff --git a/plugins/paintops/defaultpaintops/brush/KisDabRenderingQueue.cpp b/plugins/paintops/defaultpaintops/brush/KisDabRenderingQueue.cpp
index 26d1d01383..2a8417a5f0 100644
--- a/plugins/paintops/defaultpaintops/brush/KisDabRenderingQueue.cpp
+++ b/plugins/paintops/defaultpaintops/brush/KisDabRenderingQueue.cpp
@@ -1,459 +1,461 @@
 /*
  *  Copyright (c) 2017 Dmitry Kazakov <dimula73@gmail.com>
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
  *  the Free Software Foundation; either version 2 of the License, or
  *  (at your option) any later version.
  *
  *  This program is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *  GNU General Public License for more details.
  *
  *  You should have received a copy of the GNU General Public License
  *  along with this program; if not, write to the Free Software
  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  */
 
 #include "KisDabRenderingQueue.h"
 
 #include "KisDabRenderingJob.h"
 #include "KisRenderedDab.h"
 #include "kis_painter.h"
 
 #include <QSet>
 #include <QMutex>
 #include <QMutexLocker>
 #include <KisRollingMeanAccumulatorWrapper.h>
 
 #include "kis_algebra_2d.h"
 
 struct KisDabRenderingQueue::Private
 {
     struct DumbCacheInterface : public CacheInterface {
         void getDabType(bool hasDabInCache,
                                 KisDabCacheUtils::DabRenderingResources *resources,
                                 const KisDabCacheUtils::DabRequestInfo &request,
                                 /* out */
                                 KisDabCacheUtils::DabGenerationInfo *di,
                                 bool *shouldUseCache) override
         {
             Q_UNUSED(hasDabInCache);
             Q_UNUSED(resources);
             Q_UNUSED(request);
 
             di->needsPostprocessing = false;
             *shouldUseCache = false;
         }
 
         bool hasSeparateOriginal(KisDabCacheUtils::DabRenderingResources *resources) const override
         {
             Q_UNUSED(resources);
             return false;
         }
 
     };
 
     Private(const KoColorSpace *_colorSpace,
             KisDabCacheUtils::ResourcesFactory _resourcesFactory)
         : cacheInterface(new DumbCacheInterface),
           colorSpace(_colorSpace),
           resourcesFactory(_resourcesFactory),
           avgExecutionTime(50),
           avgDabSize(50)
     {
         KIS_SAFE_ASSERT_RECOVER_NOOP(resourcesFactory);
     }
 
     ~Private() {
         qDeleteAll(cachedResources);
         cachedResources.clear();
     }
 
     QList<KisDabRenderingJobSP> jobs;
     int nextSeqNoToUse = 0;
     int lastPaintedJob = -1;
     int lastDabJobInQueue = -1;
     QScopedPointer<CacheInterface> cacheInterface;
     const KoColorSpace *colorSpace;
     qreal averageOpacity = 0.0;
 
     KisDabCacheUtils::ResourcesFactory resourcesFactory;
 
     QList<KisDabCacheUtils::DabRenderingResources*> cachedResources;
     QSet<KisFixedPaintDeviceSP> cachedPaintDevices;
 
     QMutex mutex;
 
     KisRollingMeanAccumulatorWrapper avgExecutionTime;
     KisRollingMeanAccumulatorWrapper avgDabSize;
 
     int calculateLastDabJobIndex(int startSearchIndex);
     void cleanPaintedDabs();
     bool dabsHaveSeparateOriginal();
 
     KisDabCacheUtils::DabRenderingResources* fetchResourcesFromCache();
     void putResourcesToCache(KisDabCacheUtils::DabRenderingResources *resources);
 };
 
 
 KisDabRenderingQueue::KisDabRenderingQueue(const KoColorSpace *cs,
                                            KisDabCacheUtils::ResourcesFactory resourcesFactory)
     : m_d(new Private(cs, resourcesFactory))
 {
 }
 
 KisDabRenderingQueue::~KisDabRenderingQueue()
 {
 }
 
 int KisDabRenderingQueue::Private::calculateLastDabJobIndex(int startSearchIndex)
 {
     if (startSearchIndex < 0) {
         startSearchIndex = jobs.size() - 1;
     }
 
     // try to use cached value
     if (startSearchIndex >= lastDabJobInQueue) {
         return lastDabJobInQueue;
     }
 
     // if we are below the cached value, just iterate through the dabs
     // (which is extremely(!) slow)
     for (int i = startSearchIndex; i >= 0; i--) {
         if (jobs[i]->type == KisDabRenderingJob::Dab) {
             return i;
         }
     }
 
     return -1;
 }
 
 KisDabRenderingJobSP KisDabRenderingQueue::addDab(const KisDabCacheUtils::DabRequestInfo &request,
                                                  qreal opacity, qreal flow)
 {
     QMutexLocker l(&m_d->mutex);
 
     const int seqNo = m_d->nextSeqNoToUse++;
 
     KisDabCacheUtils::DabRenderingResources *resources = m_d->fetchResourcesFromCache();
     KIS_SAFE_ASSERT_RECOVER_RETURN_VALUE(resources, KisDabRenderingJobSP());
 
     // We should sync the cached brush into the current seqNo
     resources->syncResourcesToSeqNo(seqNo, request.info);
 
     const int lastDabJobIndex = m_d->lastDabJobInQueue;
 
     KisDabRenderingJobSP job(new KisDabRenderingJob());
 
     bool shouldUseCache = false;
     m_d->cacheInterface->getDabType(lastDabJobIndex >= 0,
                                     resources,
                                     request,
                                     &job->generationInfo,
                                     &shouldUseCache);
 
     m_d->putResourcesToCache(resources);
     resources = 0;
 
     // TODO: initialize via c-tor
     job->seqNo = seqNo;
     job->type =
         !shouldUseCache ? KisDabRenderingJob::Dab :
         job->generationInfo.needsPostprocessing ? KisDabRenderingJob::Postprocess :
         KisDabRenderingJob::Copy;
     job->opacity = opacity;
     job->flow = flow;
 
 
     if (job->type == KisDabRenderingJob::Dab) {
         job->status = KisDabRenderingJob::Running;
     } else if (job->type == KisDabRenderingJob::Postprocess ||
                job->type == KisDabRenderingJob::Copy) {
 
         KIS_SAFE_ASSERT_RECOVER_RETURN_VALUE(lastDabJobIndex >= 0, KisDabRenderingJobSP());
+        KIS_SAFE_ASSERT_RECOVER_RETURN_VALUE(lastDabJobIndex < m_d->jobs.size(), KisDabRenderingJobSP());
 
         if (m_d->jobs[lastDabJobIndex]->status == KisDabRenderingJob::Completed) {
             if (job->type == KisDabRenderingJob::Postprocess) {
                 job->status = KisDabRenderingJob::Running;
                 job->originalDevice = m_d->jobs[lastDabJobIndex]->originalDevice;
             } else if (job->type == KisDabRenderingJob::Copy) {
                 job->status = KisDabRenderingJob::Completed;
                 job->originalDevice = m_d->jobs[lastDabJobIndex]->originalDevice;
                 job->postprocessedDevice = m_d->jobs[lastDabJobIndex]->postprocessedDevice;
             }
         }
     }
 
     m_d->jobs.append(job);
 
     KisDabRenderingJobSP jobToRun;
     if (job->status == KisDabRenderingJob::Running) {
         jobToRun = job;
     }
 
     if (job->type == KisDabRenderingJob::Dab) {
         m_d->lastDabJobInQueue = m_d->jobs.size() - 1;
         m_d->cleanPaintedDabs();
     }
 
     // collect some statistics about the dab
     m_d->avgDabSize(KisAlgebra2D::maxDimension(job->generationInfo.dstDabRect));
 
     return jobToRun;
 }
 
 QList<KisDabRenderingJobSP> KisDabRenderingQueue::notifyJobFinished(int seqNo, int usecsTime)
 {
     QMutexLocker l(&m_d->mutex);
 
     QList<KisDabRenderingJobSP> dependentJobs;
 
     /**
      * Here we use binary search for locating the necessary original dab
      */
     auto finishedJobIt =
         std::lower_bound(m_d->jobs.begin(), m_d->jobs.end(), seqNo,
                          [] (KisDabRenderingJobSP job, int seqNo) {
                              return job->seqNo < seqNo;
                          });
 
     KIS_SAFE_ASSERT_RECOVER_RETURN_VALUE(finishedJobIt != m_d->jobs.end(), dependentJobs);
     KisDabRenderingJobSP finishedJob = *finishedJobIt;
 
     KIS_SAFE_ASSERT_RECOVER_NOOP(finishedJob->status == KisDabRenderingJob::Running);
     KIS_SAFE_ASSERT_RECOVER_NOOP(finishedJob->seqNo == seqNo);
     KIS_SAFE_ASSERT_RECOVER_NOOP(finishedJob->originalDevice);
     KIS_SAFE_ASSERT_RECOVER_NOOP(finishedJob->postprocessedDevice);
 
     finishedJob->status = KisDabRenderingJob::Completed;
 
     if (finishedJob->type == KisDabRenderingJob::Dab) {
         for (auto it = finishedJobIt + 1; it != m_d->jobs.end(); ++it) {
             KisDabRenderingJobSP j = *it;
 
             // next dab job closes the chain
             if (j->type == KisDabRenderingJob::Dab) break;
 
             // the non 'dab'-type job couldn't have
             // been started before the source ob was completed
             KIS_SAFE_ASSERT_RECOVER_BREAK(j->status == KisDabRenderingJob::New);
 
             if (j->type == KisDabRenderingJob::Copy) {
 
                 j->originalDevice = finishedJob->originalDevice;
                 j->postprocessedDevice = finishedJob->postprocessedDevice;
                 j->status = KisDabRenderingJob::Completed;
 
             } else if (j->type == KisDabRenderingJob::Postprocess) {
 
                 j->originalDevice = finishedJob->originalDevice;
                 j->status = KisDabRenderingJob::Running;
                 dependentJobs << j;
             }
         }
     }
 
     if (usecsTime >= 0) {
         m_d->avgExecutionTime(usecsTime);
     }
 
     return dependentJobs;
 }
 
 void KisDabRenderingQueue::Private::cleanPaintedDabs()
 {
     const int nextToBePainted = lastPaintedJob + 1;
     const int lastSourceJob = calculateLastDabJobIndex(qMin(nextToBePainted, jobs.size() - 1));
 
     if (lastPaintedJob >= 0) {
         int numRemovedJobs = 0;
         int numRemovedJobsBeforeLastSource = 0;
 
         auto it = jobs.begin();
         for (int i = 0; i <= lastPaintedJob; i++) {
             KisDabRenderingJobSP job = *it;
 
             if (i < lastSourceJob || job->type != KisDabRenderingJob::Dab){
 
                 // cache unique 'original' devices
                 if (job->type == KisDabRenderingJob::Dab &&
                     job->postprocessedDevice != job->originalDevice) {
+
                     cachedPaintDevices << job->originalDevice;
                     job->originalDevice = 0;
                 }
 
                 it = jobs.erase(it);
                 numRemovedJobs++;
-                if (i < lastSourceJob) {
+                if (i < lastDabJobInQueue) {
                     numRemovedJobsBeforeLastSource++;
                 }
 
             } else  {
                 ++it;
             }
         }
 
         KIS_SAFE_ASSERT_RECOVER_RETURN(jobs.size() > 0);
 
         lastPaintedJob -= numRemovedJobs;
         lastDabJobInQueue -= numRemovedJobsBeforeLastSource;
     }
 }
 
 QList<KisRenderedDab> KisDabRenderingQueue::takeReadyDabs(bool returnMutableDabs)
 {
     QMutexLocker l(&m_d->mutex);
 
     QList<KisRenderedDab> renderedDabs;
     if (m_d->jobs.isEmpty()) return renderedDabs;
 
     KIS_SAFE_ASSERT_RECOVER_NOOP(
         m_d->jobs.isEmpty() ||
         m_d->jobs.first()->type == KisDabRenderingJob::Dab);
 
     const int copyJobAfterInclusive =
         returnMutableDabs && !m_d->dabsHaveSeparateOriginal() ?
             m_d->lastDabJobInQueue :
             std::numeric_limits<int>::max();
 
     for (int i = 0; i < m_d->jobs.size(); i++) {
         KisDabRenderingJobSP j = m_d->jobs[i];
 
         if (j->status != KisDabRenderingJob::Completed) break;
 
         if (i <= m_d->lastPaintedJob) continue;
 
         KisRenderedDab dab;
         KisFixedPaintDeviceSP resultDevice = j->postprocessedDevice;
 
         if (i >= copyJobAfterInclusive) {
             resultDevice = new KisFixedPaintDevice(*resultDevice);
         }
 
         dab.device = resultDevice;
         dab.offset = j->dstDabOffset();
         dab.opacity = j->opacity;
         dab.flow = j->flow;
 
         m_d->averageOpacity = KisPainter::blendAverageOpacity(j->opacity, m_d->averageOpacity);
         dab.averageOpacity = m_d->averageOpacity;
 
 
         renderedDabs.append(dab);
 
         m_d->lastPaintedJob = i;
     }
 
     m_d->cleanPaintedDabs();
     return renderedDabs;
 }
 
 bool KisDabRenderingQueue::hasPreparedDabs() const
 {
     QMutexLocker l(&m_d->mutex);
 
     const int nextToBePainted = m_d->lastPaintedJob + 1;
 
     return
         nextToBePainted >= 0 &&
         nextToBePainted < m_d->jobs.size() &&
             m_d->jobs[nextToBePainted]->status == KisDabRenderingJob::Completed;
 }
 
 void KisDabRenderingQueue::setCacheInterface(KisDabRenderingQueue::CacheInterface *interface)
 {
     m_d->cacheInterface.reset(interface);
 }
 
 KisFixedPaintDeviceSP KisDabRenderingQueue::fetchCachedPaintDevce()
 {
     QMutexLocker l(&m_d->mutex);
 
     KisFixedPaintDeviceSP result;
 
     if (m_d->cachedPaintDevices.isEmpty()) {
         result = new KisFixedPaintDevice(m_d->colorSpace);
     } else {
         // there is no difference from which side to take elements from QSet
         auto it = m_d->cachedPaintDevices.begin();
         result = *it;
         m_d->cachedPaintDevices.erase(it);
     }
 
     return result;
 }
 
 void KisDabRenderingQueue::recyclePaintDevicesForCache(const QVector<KisFixedPaintDeviceSP> devices)
 {
     QMutexLocker l(&m_d->mutex);
 
     Q_FOREACH (KisFixedPaintDeviceSP device, devices) {
         // the set automatically checks if the device is unique in the set
         m_d->cachedPaintDevices << device;
     }
 }
 
 int KisDabRenderingQueue::averageExecutionTime() const
 {
     QMutexLocker l(&m_d->mutex);
     return qRound(m_d->avgExecutionTime.rollingMean());
 }
 
 int KisDabRenderingQueue::averageDabSize() const
 {
     QMutexLocker l(&m_d->mutex);
     return qRound(m_d->avgDabSize.rollingMean());
 }
 
 bool KisDabRenderingQueue::Private::dabsHaveSeparateOriginal()
 {
     KisDabCacheUtils::DabRenderingResources *resources = fetchResourcesFromCache();
 
     const bool result = cacheInterface->hasSeparateOriginal(resources);
 
     putResourcesToCache(resources);
 
     return result;
 }
 
 KisDabCacheUtils::DabRenderingResources *KisDabRenderingQueue::Private::fetchResourcesFromCache()
 {
     KisDabCacheUtils::DabRenderingResources *resources = 0;
 
     // fetch/create a temporary resources object
     if (!cachedResources.isEmpty()) {
         resources = cachedResources.takeLast();
     } else {
         resources = resourcesFactory();
     }
 
     return resources;
 }
 
 void KisDabRenderingQueue::Private::putResourcesToCache(KisDabCacheUtils::DabRenderingResources *resources)
 {
     cachedResources << resources;
 }
 
 KisDabCacheUtils::DabRenderingResources *KisDabRenderingQueue::fetchResourcesFromCache()
 {
     // TODO: make a separate lock for that
     QMutexLocker l(&m_d->mutex);
     return m_d->fetchResourcesFromCache();
 }
 
 void KisDabRenderingQueue::putResourcesToCache(KisDabCacheUtils::DabRenderingResources *resources)
 {
     QMutexLocker l(&m_d->mutex);
     m_d->putResourcesToCache(resources);
 }
 
 int KisDabRenderingQueue::testingGetQueueSize() const
 {
     QMutexLocker l(&m_d->mutex);
 
     return m_d->jobs.size();
 }