Version:            (using KDE 4.3.3)
Compiler:          g++ 4.3.4 
OS:                Linux
Installed from:    Debian testing/unstable Packages

Steps to reproduce with plasmoidviewer (100% reproducible on my system with either KDE 4.3.2 or 4.3.3).

Steps below (order is important!). Start with an empty taskbar.

* Start akregator
* Start konqueror
* Start `plasmoidviewer tasks`
* Start another konqueror instance.

After you do this, tasks widget in plasmoidviewer should span two rows with akregator and two konqueror instances (grouped) being on the first row and plasmoidviewer itself on the second row. Then

* Close the 2nd (or any, not sure) konqueror instance.

Watch plasmoidviewer crash. Backtrace below:

Application: Plasma valdiklių žiūryklė (plasmoidviewer), signal: Segmentation fault
The current source language is "auto; currently c".
[KCrash Handler]
#5  QGraphicsSceneFindItemBspTreeVisitor::visit (this=0x1f248f0, items=0x20a6ac0) at graphicsview/qgraphicsscene_bsp.cpp:79
#6  0x00007f7149e3a628 in QGraphicsSceneBspTree::climbTree (this=0x1f24810, visitor=0x1f248f0, rect=..., index=<value optimized out>) at graphicsview/qgraphicsscene_bsp.cpp:261
#7  0x00007f7149e3a6d2 in QGraphicsSceneBspTree::climbTree (this=0x1f24810, visitor=0x1f248f0, rect=..., index=<value optimized out>) at graphicsview/qgraphicsscene_bsp.cpp:252
#8  0x00007f7149e3a628 in QGraphicsSceneBspTree::climbTree (this=0x1f24810, visitor=0x1f248f0, rect=..., index=<value optimized out>) at graphicsview/qgraphicsscene_bsp.cpp:261
#9  0x00007f7149e3a628 in QGraphicsSceneBspTree::climbTree (this=0x1f24810, visitor=0x1f248f0, rect=..., index=<value optimized out>) at graphicsview/qgraphicsscene_bsp.cpp:261
#10 0x00007f7149e3ab40 in QGraphicsSceneBspTree::items (this=0x0, rect=..., onlyTopLevelItems=<value optimized out>) at graphicsview/qgraphicsscene_bsp.cpp:154
#11 0x00007f7149e3e2a9 in QGraphicsSceneBspTreeIndexPrivate::estimateItems (this=0x1f24760, rect=..., order=Qt::AscendingOrder, onlyTopLevelItems=true)
    at graphicsview/qgraphicsscenebsptreeindex.cpp:387
#12 0x00007f7149e3e483 in QGraphicsSceneBspTreeIndex::estimateTopLevelItems (this=<value optimized out>, rect=..., order=34828000) at graphicsview/qgraphicsscenebsptreeindex.cpp:604
#13 0x00007f7149e2badb in QGraphicsScenePrivate::drawItems (this=0x1f25ff0, painter=0x7fffd65221e0, viewTransform=0x0, exposedRegion=0x1f12c40, widget=0x1f25920)
    at graphicsview/qgraphicsscene.cpp:4476
#14 0x00007f7149e4e544 in QGraphicsView::paintEvent (this=0x7fffd6524700, event=<value optimized out>) at graphicsview/qgraphicsview.cpp:3308
#15 0x00007f7149877661 in QWidget::event (this=0x7fffd6524700, event=0x7fffd6522a50) at kernel/qwidget.cpp:8050
#16 0x00007f7149c17ddb in QFrame::event (this=0x7fffd6524700, e=0x7fffd6522a50) at widgets/qframe.cpp:557
#17 0x00007f7149e4ce43 in QGraphicsView::viewportEvent (this=0x7fffd6524700, event=0x7fffd6522a50) at graphicsview/qgraphicsview.cpp:2708
#18 0x00007f714a469fc8 in QCoreApplicationPrivate::sendThroughObjectEventFilters (this=<value optimized out>, receiver=0x1f25920, event=0x7fffd6522a50) at kernel/qcoreapplication.cpp:819
#19 0x00007f7149822cfc in QApplicationPrivate::notify_helper (this=0x1d8d680, receiver=0x1f25920, e=0x7fffd6522a50) at kernel/qapplication.cpp:4273
#20 0x00007f714982a1c9 in QApplication::notify (this=0x7fffd6524780, receiver=0x1f25920, e=0x7fffd6522a50) at kernel/qapplication.cpp:4166
#21 0x00007f714b25648b in KApplication::notify (this=0x7fffd6524780, receiver=0x1f25920, event=0x7fffd6522a50) at ../../kdeui/kernel/kapplication.cpp:302
#22 0x00007f714a46ab9c in QCoreApplication::notifyInternal (this=0x7fffd6524780, receiver=0x1f25920, event=0x7fffd6522a50) at kernel/qcoreapplication.cpp:704
#23 0x00007f714987fb9f in QCoreApplication::sendSpontaneousEvent (this=0x1f25c70, pdev=0x1f2ab28, rgn=..., offset=..., flags=68, sharedPainter=0x0, backingStore=0x20a3540)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:218
#24 QWidgetPrivate::drawWidget (this=0x1f25c70, pdev=0x1f2ab28, rgn=..., offset=..., flags=68, sharedPainter=0x0, backingStore=0x20a3540) at kernel/qwidget.cpp:5276
#25 0x00007f7149a3056e in QWidgetBackingStore::sync (this=0x20a3540) at painting/qbackingstore.cpp:1280
#26 0x00007f7149871010 in QWidgetPrivate::syncBackingStore (this=0x1f12780) at kernel/qwidget.cpp:1661
#27 0x00007f7149877d68 in QWidget::event (this=0x7fffd6524700, event=0x240af80) at kernel/qwidget.cpp:8196
#28 0x00007f7149c17ddb in QFrame::event (this=0x7fffd6524700, e=0x240af80) at widgets/qframe.cpp:557
#29 0x00007f7149ca1ddb in QAbstractScrollArea::event (this=0x7fffd6524700, e=0x240af80) at widgets/qabstractscrollarea.cpp:944
#30 0x00007f7149822d2d in QApplicationPrivate::notify_helper (this=0x1d8d680, receiver=0x7fffd6524700, e=0x240af80) at kernel/qapplication.cpp:4277
#31 0x00007f714982a1c9 in QApplication::notify (this=0x7fffd6524780, receiver=0x7fffd6524700, e=0x240af80) at kernel/qapplication.cpp:4166
#32 0x00007f714b25648b in KApplication::notify (this=0x7fffd6524780, receiver=0x7fffd6524700, event=0x240af80) at ../../kdeui/kernel/kapplication.cpp:302
#33 0x00007f714a46ab9c in QCoreApplication::notifyInternal (this=0x7fffd6524780, receiver=0x7fffd6524700, event=0x240af80) at kernel/qcoreapplication.cpp:704
#34 0x00007f714a46ba7c in QCoreApplication::sendEvent (receiver=0x7fffd6524700, event_type=77, data=0x1d75de0) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:215
#35 QCoreApplicationPrivate::sendPostedEvents (receiver=0x7fffd6524700, event_type=77, data=0x1d75de0) at kernel/qcoreapplication.cpp:1345
#36 0x00007f7149e37809 in QGraphicsViewPrivate::dispatchPendingUpdateRequests (this=0x1f25ff0) at ../../include/QtGui/private/../../../src/gui/graphicsview/qgraphicsview_p.h:178
#37 QGraphicsScenePrivate::_q_processDirtyItems (this=0x1f25ff0) at graphicsview/qgraphicsscene.cpp:476
#38 0x00007f7149e37cba in QGraphicsScene::qt_metacall (this=0x7fffd6524728, _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, _a=0x23c2090)
    at .moc/release-shared/moc_qgraphicsscene.cpp:128
#39 0x00007f714acda015 in Plasma::Corona::qt_metacall (this=0x0, _c=QMetaObject::QueryPropertyStored, _id=0, _a=0x2136ee0) at ./corona.moc:101
#40 0x00007f714a47ac88 in QObject::event (this=0x7fffd6524728, e=0x20457d0) at kernel/qobject.cpp:1246
#41 0x00007f7149e32b52 in QGraphicsScene::event (this=0x7fffd6524728, event=0x20457d0) at graphicsview/qgraphicsscene.cpp:3366
#42 0x00007f7149822d2d in QApplicationPrivate::notify_helper (this=0x1d8d680, receiver=0x7fffd6524728, e=0x20457d0) at kernel/qapplication.cpp:4277
#43 0x00007f714982a1c9 in QApplication::notify (this=0x7fffd6524780, receiver=0x7fffd6524728, e=0x20457d0) at kernel/qapplication.cpp:4166
#44 0x00007f714b25648b in KApplication::notify (this=0x7fffd6524780, receiver=0x7fffd6524728, event=0x20457d0) at ../../kdeui/kernel/kapplication.cpp:302
#45 0x00007f714a46ab9c in QCoreApplication::notifyInternal (this=0x7fffd6524780, receiver=0x7fffd6524728, event=0x20457d0) at kernel/qcoreapplication.cpp:704
#46 0x00007f714a46ba7c in QCoreApplication::sendEvent (receiver=0x0, event_type=0, data=0x1d75de0) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:215
#47 QCoreApplicationPrivate::sendPostedEvents (receiver=0x0, event_type=0, data=0x1d75de0) at kernel/qcoreapplication.cpp:1345
#48 0x00007f71498cb426 in QCoreApplication::sendPostedEvents (this=0x1d75b60, flags=...) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:220
#49 QEventDispatcherX11::processEvents (this=0x1d75b60, flags=...) at kernel/qeventdispatcher_x11.cpp:75
#50 0x00007f714a4694a2 in QEventLoop::processEvents (this=<value optimized out>, flags=...) at kernel/qeventloop.cpp:149
#51 0x00007f714a469874 in QEventLoop::exec (this=0x7fffd65244a0, flags=...) at kernel/qeventloop.cpp:201
#52 0x00007f714a46bd06 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:981
#53 0x0000000000408a49 in main (argc=2, argv=0x7fffd65250c8) at ../../../../plasma/shells/plasmoidviewer/main.cpp:164