diff --git a/libs/ui/kis_animation_frame_cache.cpp b/libs/ui/kis_animation_frame_cache.cpp
index f377acf40d..026e70f2cf 100644
--- a/libs/ui/kis_animation_frame_cache.cpp
+++ b/libs/ui/kis_animation_frame_cache.cpp
@@ -1,410 +1,412 @@
 /*
  *  Copyright (c) 2015 Jouni Pentikäinen <joupent@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 "kis_animation_frame_cache.h"
 
 #include <QMap>
 
 #include "kis_debug.h"
 
 #include "kis_image.h"
 #include "kis_image_animation_interface.h"
 #include "kis_time_range.h"
 #include "KisPart.h"
 #include "kis_animation_cache_populator.h"
 
 #include <KisAbstractFrameCacheSwapper.h>
 #include "KisFrameCacheSwapper.h"
 #include "KisInMemoryFrameCacheSwapper.h"
 
 #include "kis_image_config.h"
 #include "kis_config_notifier.h"
 
 #include "opengl/kis_opengl_image_textures.h"
 
 #include <kis_algebra_2d.h>
 #include <cmath>
 
 
 struct KisAnimationFrameCache::Private
 {
     Private(KisOpenGLImageTexturesSP _textures)
         : textures(_textures)
     {
         image = textures->image();
     }
 
     ~Private()
     {
     }
 
     KisOpenGLImageTexturesSP textures;
     KisImageWSP image;
 
     QScopedPointer<KisAbstractFrameCacheSwapper> swapper;
     int frameSizeLimit = 777;
 
     KisOpenGLUpdateInfoSP fetchFrameDataImpl(KisImageSP image, const QRect &requestedRect, int lod);
 
     struct Frame
     {
         KisOpenGLUpdateInfoSP openGlFrame;
         int length;
 
         Frame(KisOpenGLUpdateInfoSP info, int length)
             : openGlFrame(info), length(length)
         {}
     };
 
     QMap<int, int> newFrames;
 
     int getFrameIdAtTime(int time) const
     {
         if (newFrames.isEmpty()) return -1;
 
         auto it = newFrames.upperBound(time);
 
         if (it != newFrames.constBegin()) it--;
 
         KIS_SAFE_ASSERT_RECOVER_RETURN_VALUE(it != newFrames.constEnd(), 0);
         const int start = it.key();
         const int length = it.value();
 
         bool foundFrameValid = false;
 
         if (length == -1) {
             if (start <= time) {
                 foundFrameValid = true;
             }
         } else {
             int end = start + length - 1;
             if (start <= time && time <= end) {
                 foundFrameValid = true;
             }
         }
 
         return foundFrameValid ? start : -1;
     }
 
     bool hasFrame(int time) const {
         return getFrameIdAtTime(time) >= 0;
     }
 
     KisOpenGLUpdateInfoSP getFrame(int time)
     {
         const int frameId = getFrameIdAtTime(time);
         return frameId >= 0 ? swapper->loadFrame(frameId) : 0;
     }
 
     void addFrame(KisOpenGLUpdateInfoSP info, const KisTimeRange& range)
     {
         invalidate(range);
 
         const int length = range.isInfinite() ? -1 : range.end() - range.start() + 1;
         newFrames.insert(range.start(), length);
         swapper->saveFrame(range.start(), info, image->bounds());
     }
 
     /**
      * Invalidate any cached frames within the given time range.
      * @param range
      * @return true if frames were invalidated, false if nothing was changed
      */
     bool invalidate(const KisTimeRange& range)
     {
         if (newFrames.isEmpty()) return false;
 
         bool cacheChanged = false;
 
         auto it = newFrames.lowerBound(range.start());
         if (it.key() != range.start() && it != newFrames.begin()) it--;
 
         while (it != newFrames.end()) {
             const int start = it.key();
             const int length = it.value();
             const bool frameIsInfinite = (length == -1);
             const int end = start + length - 1;
 
             if (start >= range.start()) {
                 if (!range.isInfinite() && start > range.end()) {
                     break;
                 }
 
                 if (!range.isInfinite() && (frameIsInfinite || end > range.end())) {
                     // Reinsert with a later start
                     int newStart = range.end() + 1;
                     int newLength = frameIsInfinite ? -1 : (end - newStart + 1);
 
                     newFrames.insert(newStart, newLength);
                     swapper->moveFrame(start, newStart);
                 } else {
                     swapper->forgetFrame(start);
                 }
 
                 it = newFrames.erase(it);
 
                 cacheChanged = true;
                 continue;
 
             } else if (frameIsInfinite || end >= range.start()) {
                 const int newEnd = range.start() - 1;
                 *it = newEnd - start + 1;
 
                 cacheChanged = true;
             }
 
             it++;
         }
 
         return cacheChanged;
     }
 
     int effectiveLevelOfDetail(const QRect &rc) const {
         if (!frameSizeLimit) return 0;
 
         const int maxDimension = KisAlgebra2D::maxDimension(rc);
 
         const qreal minLod = -std::log2(qreal(frameSizeLimit) / maxDimension);
         const int lodLimit = qMax(0, qCeil(minLod));
         return lodLimit;
     }
 
 
     // TODO: verify that we don't have any leak here!
     typedef QMap<KisOpenGLImageTexturesSP, KisAnimationFrameCache*> CachesMap;
     static CachesMap caches;
 };
 
 KisAnimationFrameCache::Private::CachesMap KisAnimationFrameCache::Private::caches;
 
 KisAnimationFrameCacheSP KisAnimationFrameCache::getFrameCache(KisOpenGLImageTexturesSP textures)
 {
     KisAnimationFrameCache *cache;
 
     Private::CachesMap::iterator it = Private::caches.find(textures);
     if (it == Private::caches.end()) {
         cache = new KisAnimationFrameCache(textures);
         Private::caches.insert(textures, cache);
     } else {
         cache = it.value();
     }
 
     return cache;
 }
 
 const QList<KisAnimationFrameCache *> KisAnimationFrameCache::caches()
 {
     return Private::caches.values();
 }
 
 KisAnimationFrameCache::KisAnimationFrameCache(KisOpenGLImageTexturesSP textures)
     : m_d(new Private(textures))
 {
     // create swapping backend
     slotConfigChanged();
 
     connect(m_d->image->animationInterface(), SIGNAL(sigFramesChanged(KisTimeRange,QRect)), this, SLOT(framesChanged(KisTimeRange,QRect)));
     connect(KisConfigNotifier::instance(), SIGNAL(configChanged()), SLOT(slotConfigChanged()));
 }
 
 KisAnimationFrameCache::~KisAnimationFrameCache()
 {
     Private::caches.remove(m_d->textures);
 }
 
 bool KisAnimationFrameCache::uploadFrame(int time)
 {
     KisOpenGLUpdateInfoSP info = m_d->getFrame(time);
 
     if (!info) {
         // Do nothing!
         //
         // Previously we were trying to start cache regeneration in this point,
         // but it caused even bigger slowdowns when scrubbing
     } else {
         m_d->textures->recalculateCache(info);
     }
 
     return bool(info);
 }
 
 bool KisAnimationFrameCache::shouldUploadNewFrame(int newTime, int oldTime) const
 {
     if (oldTime < 0) return true;
 
     const int oldKeyframeStart = m_d->getFrameIdAtTime(oldTime);
     if (oldKeyframeStart < 0) return true;
 
     const int oldKeyFrameLength = m_d->newFrames[oldKeyframeStart];
     return !(newTime >= oldKeyframeStart && (newTime < oldKeyframeStart + oldKeyFrameLength || oldKeyFrameLength == -1));
 }
 
 KisAnimationFrameCache::CacheStatus KisAnimationFrameCache::frameStatus(int time) const
 {
     return m_d->hasFrame(time) ? Cached : Uncached;
 }
 
 KisImageWSP KisAnimationFrameCache::image()
 {
     return m_d->image;
 }
 
 void KisAnimationFrameCache::framesChanged(const KisTimeRange &range, const QRect &rect)
 {
     Q_UNUSED(rect);
 
     if (!range.isValid()) return;
 
     bool cacheChanged = m_d->invalidate(range);
 
     if (cacheChanged) {
         emit changed();
     }
 }
 
 void KisAnimationFrameCache::slotConfigChanged()
 {
     m_d->newFrames.clear();
 
     KisImageConfig cfg;
 
     if (cfg.useOnDiskAnimationCacheSwapping()) {
         m_d->swapper.reset(new KisFrameCacheSwapper(m_d->textures->updateInfoBuilder(), cfg.swapDir()));
     } else {
         m_d->swapper.reset(new KisInMemoryFrameCacheSwapper());
     }
 
     m_d->frameSizeLimit = cfg.useAnimationCacheFrameSizeLimit() ? cfg.animationCacheFrameSizeLimit() : 0;
     emit changed();
 }
 
 KisOpenGLUpdateInfoSP KisAnimationFrameCache::Private::fetchFrameDataImpl(KisImageSP image, const QRect &requestedRect, int lod)
 {
     if (lod > 0) {
         KisPaintDeviceSP tempDevice = new KisPaintDevice(image->projection()->colorSpace());
         tempDevice->prepareClone(image->projection());
         image->projection()->generateLodCloneDevice(tempDevice, image->projection()->extent(), lod);
 
         const QRect fetchRect = KisLodTransform::alignedRect(requestedRect, lod);
         return textures->updateInfoBuilder().buildUpdateInfo(fetchRect, tempDevice, image->bounds(), lod, true);
     } else {
         return textures->updateCache(requestedRect, image);
     }
 }
 
 KisOpenGLUpdateInfoSP KisAnimationFrameCache::fetchFrameData(int time, KisImageSP image, const QRegion &requestedRegion) const
 {
     if (time != image->animationInterface()->currentTime()) {
         qWarning() << "WARNING: KisAnimationFrameCache::frameReady image's time doesn't coincide with the requested time!";
         qWarning() << "    "  << ppVar(image->animationInterface()->currentTime()) << ppVar(time);
     }
 
     // the frames are always generated at full scale
     KIS_SAFE_ASSERT_RECOVER_NOOP(image->currentLevelOfDetail() == 0);
 
     const int lod = m_d->effectiveLevelOfDetail(requestedRegion.boundingRect());
 
     KisOpenGLUpdateInfoSP totalInfo;
 
     Q_FOREACH (const QRect &rc, requestedRegion.rects()) {
         KisOpenGLUpdateInfoSP info = m_d->fetchFrameDataImpl(image, rc, lod);
         if (!totalInfo) {
             totalInfo = info;
         } else {
             const bool result = totalInfo->tryMergeWith(*info);
             KIS_SAFE_ASSERT_RECOVER_NOOP(result);
         }
     }
 
     return totalInfo;
 }
 
 void KisAnimationFrameCache::addConvertedFrameData(KisOpenGLUpdateInfoSP info, int time)
 {
     KisTimeRange identicalRange = KisTimeRange::infinite(0);
     KisTimeRange::calculateTimeRangeRecursive(m_d->image->root(), time, identicalRange, true);
 
     m_d->addFrame(info, identicalRange);
 
     emit changed();
 }
 
 void KisAnimationFrameCache::dropLowQualityFrames(const KisTimeRange &range, const QRect &regionOfInterest, const QRect &minimalRect)
 {
     if (m_d->newFrames.isEmpty()) return;
 
     auto it = m_d->newFrames.upperBound(range.start());
 
+    // the vector is guaranteed to be non-empty,
+    // so decrementing iterator is safe
     if (it != m_d->newFrames.begin()) it--;
 
-    while (it.key() <= range.end()) {
+    while (it != m_d->newFrames.end() && it.key() <= range.end()) {
         const int frameId = it.key();
         const int frameLength = it.value();
 
         if (frameId + frameLength - 1 < range.start()) {
             ++it;
             continue;
         }
 
         const QRect frameRect = m_d->swapper->frameDirtyRect(frameId);
         const int frameLod = m_d->swapper->frameLevelOfDetail(frameId);
 
         if (frameLod > m_d->effectiveLevelOfDetail(regionOfInterest) || !frameRect.contains(minimalRect)) {
             m_d->swapper->forgetFrame(frameId);
             it = m_d->newFrames.erase(it);
         } else {
             ++it;
         }
     }
 }
 
 bool KisAnimationFrameCache::framesHaveValidRoi(const KisTimeRange &range, const QRect &regionOfInterest)
 {
     if (m_d->newFrames.isEmpty()) return false;
 
     auto it = m_d->newFrames.upperBound(range.start());
 
     if (it != m_d->newFrames.begin()) it--;
 
     int expectedNextFrameStart = it.key();
 
     while (it.key() <= range.end()) {
         const int frameId = it.key();
         const int frameLength = it.value();
 
         if (frameId + frameLength - 1 < range.start()) {
             expectedNextFrameStart = frameId + frameLength;
             ++it;
             continue;
         }
 
         if (expectedNextFrameStart != frameId) {
             KIS_SAFE_ASSERT_RECOVER_NOOP(expectedNextFrameStart < frameId);
             return false;
         }
 
         if (!m_d->swapper->frameDirtyRect(frameId).contains(regionOfInterest)) {
             return false;
         }
 
         expectedNextFrameStart = frameId + frameLength;
         ++it;
     }
 
     return true;
 }