diff --git a/effects/taskbarthumbnail/taskbarthumbnail.cpp b/effects/taskbarthumbnail/taskbarthumbnail.cpp
index 4fda13e86..dc5eeda4a 100644
--- a/effects/taskbarthumbnail/taskbarthumbnail.cpp
+++ b/effects/taskbarthumbnail/taskbarthumbnail.cpp
@@ -1,154 +1,157 @@
 /********************************************************************
  KWin - the KDE window manager
  This file is part of the KDE project.
 
 Copyright (C) 2007 Rivo Laks <rivolaks@hot.ee>
 Copyright (C) 2007 Lubos Lunak <l.lunak@kde.org>
 
 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, see <http://www.gnu.org/licenses/>.
 *********************************************************************/
 
 #include "taskbarthumbnail.h"
 
 #include <kdebug.h>
 
 #ifdef KWIN_HAVE_OPENGL
 #include <kwinglutils.h>
 #endif
 
 // This effect shows a preview inside a window that has a special property set
 // on it that says which window and where to render. It is used by the taskbar
 // to show window previews in tooltips.
 
 namespace KWin
 {
 
 KWIN_EFFECT(taskbarthumbnail, TaskbarThumbnailEffect)
 
 TaskbarThumbnailEffect::TaskbarThumbnailEffect()
 {
     atom = XInternAtom(display(), "_KDE_WINDOW_PREVIEW", False);
     effects->registerPropertyType(atom, true);
     // TODO hackish way to announce support, make better after 4.0
     unsigned char dummy = 0;
     XChangeProperty(display(), rootWindow(), atom, atom, 8, PropModeReplace, &dummy, 1);
     connect(effects, SIGNAL(windowAdded(EffectWindow*)), this, SLOT(slotWindowAdded(EffectWindow*)));
     connect(effects, SIGNAL(windowDeleted(EffectWindow*)), this, SLOT(slotWindowDeleted(EffectWindow*)));
     connect(effects, SIGNAL(windowDamaged(EffectWindow*,QRect)), this, SLOT(slotWindowDamaged(EffectWindow*,QRect)));
     connect(effects, SIGNAL(propertyNotify(EffectWindow*,long)), this, SLOT(slotPropertyNotify(EffectWindow*,long)));
 }
 
 TaskbarThumbnailEffect::~TaskbarThumbnailEffect()
 {
     XDeleteProperty(display(), rootWindow(), atom);
     effects->registerPropertyType(atom, false);
 }
 
 void TaskbarThumbnailEffect::prePaintScreen(ScreenPrePaintData& data, int time)
 {
+    if (thumbnails.count() > 0) {
+        data.mask |= PAINT_SCREEN_WITH_TRANSFORMED_WINDOWS_WITHOUT_FULL_REPAINTS;
+    }
     effects->prePaintScreen(data, time);
 }
 
 void TaskbarThumbnailEffect::prePaintWindow(EffectWindow* w, WindowPrePaintData& data, int time)
 {
     // TODO what if of the windows is translucent and one not? change data.mask?
     effects->prePaintWindow(w, data, time);
 }
 
 void TaskbarThumbnailEffect::paintWindow(EffectWindow* w, int mask, QRegion region, WindowPaintData& data)
 {
     effects->paintWindow(w, mask, region, data);   // paint window first
     if (thumbnails.contains(w)) {
         // paint thumbnails on it
         int mask = PAINT_WINDOW_TRANSFORMED;
         if (data.opacity == 1.0)
             mask |= PAINT_WINDOW_OPAQUE;
         else
             mask |= PAINT_WINDOW_TRANSLUCENT;
         mask |= PAINT_WINDOW_LANCZOS;
         foreach (const Data & thumb, thumbnails.values(w)) {
             EffectWindow* thumbw = effects->findWindow(thumb.window);
             if (thumbw == NULL)
                 continue;
             WindowPaintData thumbData(thumbw);
             thumbData.opacity *= data.opacity;
             QRect r;
 
 #ifdef KWIN_HAVE_OPENGL
             if (effects->compositingType() == KWin::OpenGLCompositing) {
                 if (data.shader) {
                     thumbData.shader = data.shader;
                 }
             } // if ( effects->compositingType() == KWin::OpenGLCompositing )
 #endif
             setPositionTransformations(thumbData, r,
                                        thumbw, thumb.rect.translated(w->pos()), Qt::KeepAspectRatio);
             effects->drawWindow(thumbw, mask, r, thumbData);
         }
     }
 } // End of function
 
 void TaskbarThumbnailEffect::slotWindowDamaged(EffectWindow* w, const QRect& damage)
 {
     Q_UNUSED(damage);
     // Update the thumbnail if the window was damaged
     foreach (EffectWindow * window, thumbnails.uniqueKeys())
     foreach (const Data & thumb, thumbnails.values(window))
     if (w == effects->findWindow(thumb.window))
         window->addRepaint(thumb.rect);
 }
 
 void TaskbarThumbnailEffect::slotWindowAdded(EffectWindow* w)
 {
     slotPropertyNotify(w, atom);   // read initial value
 }
 
 void TaskbarThumbnailEffect::slotWindowDeleted(EffectWindow* w)
 {
     thumbnails.remove(w);
 }
 
 void TaskbarThumbnailEffect::slotPropertyNotify(EffectWindow* w, long a)
 {
     if (!w || a != atom)
         return;
     foreach (const Data & thumb, thumbnails.values(w)) {
         w->addRepaint(thumb.rect);
     }
     thumbnails.remove(w);
     QByteArray data = w->readProperty(atom, atom, 32);
     if (data.length() < 1)
         return;
     long* d = reinterpret_cast< long* >(data.data());
     int len = data.length() / sizeof(d[ 0 ]);
     int pos = 0;
     int cnt = d[ 0 ];
     ++pos;
     for (int i = 0;
             i < cnt;
             ++i) {
         int size = d[ pos ];
         if (len - pos < size)
             return; // format error
         ++pos;
         Data data;
         data.window = d[ pos ];
         data.rect = QRect(d[ pos + 1 ], d[ pos + 2 ], d[ pos + 3 ], d[ pos + 4 ]);
         thumbnails.insert(w, data);
         w->addRepaint(data.rect);
         pos += size;
     }
 }
 
 } // namespace