Bt from 208156: 

Application: Kontact (kontact), signal: Segmentation fault
[KCrash Handler]
#5  KCal::IncidenceBase::uid (this=0x7f4bbc01c2b0) at
/usr/include/qt4/QtCore/qatomic_x86_64.h:121
#6  0x00007f4be4e346e7 in KCal::Calendar::removeRelations (this=0x28bf230,
incidence=0x2a6a790) at /build/buildd/kdepimlibs-4.3.1/kcal/calendar.cpp:873
#7  0x00007f4be4e380dc in KCal::CalendarLocal::deleteTodo (this=0x7fff4ce582a0,
todo=0x7f4bbc01c2b0) at
/build/buildd/kdepimlibs-4.3.1/kcal/calendarlocal.cpp:267
#8  0x00007f4be4e34d81 in KCal::Incidence::DeleteVisitor<KCal::Calendar>::visit
(this=<value optimized out>, t=0x7f4bbc01c2b0) at
/build/buildd/kdepimlibs-4.3.1/kcal/incidence.h:123
#9  0x00007f4be4e2dc3a in KCal::Calendar::deleteIncidence (this=0x28bf230,
incidence=0x2a6a790) at /build/buildd/kdepimlibs-4.3.1/kcal/calendar.cpp:438
#10 0x00007f4bc5048ee1 in ?? () from /usr/lib/kde4/kcal_akonadi.so
#11 0x00007f4bc50490f0 in ?? () from /usr/lib/kde4/kcal_akonadi.so
#12 0x00007f4be13faea2 in QMetaObject::activate (sender=0x294d230,
from_signal_index=<value optimized out>, to_signal_index=6, argv=0x1) at
kernel/qobject.cpp:3113
#13 0x00007f4bc504f84a in ?? () from /usr/lib/kde4/kcal_akonadi.so
#14 0x00007f4bc505001d in ?? () from /usr/lib/kde4/kcal_akonadi.so
#15 0x00007f4bc506787a in ?? () from /usr/lib/kde4/kcal_akonadi.so
#16 0x00007f4bc504339b in ?? () from /usr/lib/kde4/kcal_akonadi.so
#17 0x00007f4bc36a8895 in ResourceItem::stateChange (this=0x2a402b0,
active=true) at /build/buildd/kdepim-4.3.1/korganizer/resourceview.cpp:197
#18 0x00007f4bc36a8912 in ResourceView::slotItemClicked (this=<value optimized
out>, i=0x2a402b0) at
/build/buildd/kdepim-4.3.1/korganizer/resourceview.cpp:817
#19 0x00007f4bc36ac611 in ResourceView::qt_metacall (this=0x2a355e0,
_c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, _a=0x7fff4ce588a0)
    at
/build/buildd/kdepim-4.3.1/obj-x86_64-linux-gnu/korganizer/resourceview.moc:121
#20 0x00007f4be13faea2 in QMetaObject::activate (sender=0x2a35520,
from_signal_index=<value optimized out>, to_signal_index=96, argv=0x1) at
kernel/qobject.cpp:3113
#21 0x00007f4be24c9120 in QTreeWidget::itemClicked (this=0x7fff4ce582a0,
_t1=0x2a402b0, _t2=0) at .moc/release-shared/moc_qtreewidget.cpp:201
#22 0x00007f4be24d6043 in QTreeWidget::qt_metacall (this=0x2a35520,
_c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, _a=0x7fff4ce589d0)
at .moc/release-shared/moc_qtreewidget.cpp:144
#23 0x00007f4be13faea2 in QMetaObject::activate (sender=0x2a35520,
from_signal_index=<value optimized out>, to_signal_index=32, argv=0x1) at
kernel/qobject.cpp:3113
#24 0x00007f4be244fbc5 in QAbstractItemView::clicked (this=0x7fff4ce582a0,
_t1=<value optimized out>) at .moc/release-shared/moc_qabstractitemview.cpp:321
#25 0x00007f4be245cbce in QAbstractItemView::mouseReleaseEvent (this=0x2a35520,
event=0x7fff4ce596f0) at itemviews/qabstractitemview.cpp:1660
#26 0x00007f4be1fb70bf in QWidget::event (this=0x2a35520, event=0x7fff4ce596f0)
at kernel/qwidget.cpp:7549
#27 0x00007f4be2329f0b in QFrame::event (this=0x2a35520, e=0x7fff4ce596f0) at
widgets/qframe.cpp:559
#28 0x00007f4be245fc0d in QAbstractItemView::viewportEvent (this=0x2a35520,
event=0x7fff4ce596f0) at itemviews/qabstractitemview.cpp:1476
#29 0x00007f4be24972d9 in QTreeView::viewportEvent (this=0x2a35520,
event=0x7fff4ce596f0) at itemviews/qtreeview.cpp:1266
#30 0x00007f4be13e49b8 in
QCoreApplicationPrivate::sendThroughObjectEventFilters (this=<value optimized
out>, receiver=0x29b4180, event=0x7fff4ce596f0) at
kernel/qcoreapplication.cpp:726
#31 0x00007f4be1f65f1c in QApplicationPrivate::notify_helper (this=0x1354da0,
receiver=0x29b4180, e=0x7fff4ce596f0) at kernel/qapplication.cpp:4052
#32 0x00007f4be1f6e8ea in QApplication::notify (this=<value optimized out>,
receiver=0x29b4180, e=0x7fff4ce596f0) at kernel/qapplication.cpp:3758
#33 0x00007f4be336adeb in KApplication::notify (this=0x7fff4ce5b640,
receiver=0x29b4180, event=0x7fff4ce596f0) at
/build/buildd/kde4libs-4.3.1/kdeui/kernel/kapplication.cpp:302
#34 0x00007f4be13e56ac in QCoreApplication::notifyInternal
(this=0x7fff4ce5b640, receiver=0x29b4180, event=0x7fff4ce596f0) at
kernel/qcoreapplication.cpp:610
#35 0x00007f4be1f6db38 in QApplicationPrivate::sendMouseEvent
(receiver=0x29b4180, event=0x7fff4ce596f0, alienWidget=0x29b4180,
nativeWidget=0x1472940, buttonDown=<value optimized out>, 
    lastMouseReceiver=@0x7f4be299d010) at
../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:216
#36 0x00007f4be1fd7b19 in QETWidget::translateMouseEvent (this=0x1472940,
event=<value optimized out>) at kernel/qapplication_x11.cpp:4409
#37 0x00007f4be1fd6b53 in QApplication::x11ProcessEvent (this=0x7fff4ce5b640,
event=0x7fff4ce5b270) at kernel/qapplication_x11.cpp:3550