Application that crashed: kontact
Version of the application: 4.3.1
KDE Version: 4.3.1 (KDE 4.3.1)
Qt Version: 4.5.2
Operating System: Linux 2.6.28-15-generic i686
Distribution: Ubuntu 9.04

What I was doing when the application crashed:
This seems to be reproducible, if all steps are done without restarting kontact:

1) Have a folder with mails (in my case, many 1000s).

2) Create a couple of subfolders for this folder, e.g. by year, with names like 2001, 2002, etc.

3) Move some mails into the subfolders. You will have to do this with the mouse, because the subfolders will not exist yet in the folder menu if you try to move them via the menu.

4) Go to a subfolder, e.g. "2001". Use search to search e.g. for the title of an E-Mail. Select the E-Mail from the search results list.

-> crash.

 -- Backtrace:
Application: Kontact (kontact), signal: Segmentation fault
[KCrash Handler]
#6  0x732d746c in ?? ()
#7  0xb0f67a1b in KMReaderWin::displayMessage (this=0xc51a5d8) at /build/buildd/kdepim-4.3.1/kmail/kmreaderwin.cpp:1605
#8  0xb0f67c30 in KMReaderWin::updateReaderWin (this=0xc4d5ff8) at /build/buildd/kdepim-4.3.1/kmail/kmreaderwin.cpp:1545
#9  0xb0f74ae8 in KMReaderWin::qt_metacall (this=0xc4d5ff8, _c=QMetaObject::InvokeMetaMethod, _id=6, _a=0xbfee8828) at /build/buildd/kdepim-4.3.1/obj-i486-linux-gnu/kmail/kmreaderwin.moc:168
#10 0xb5c651b8 in QMetaObject::activate (sender=0xc4d6050, from_signal_index=4, to_signal_index=4, argv=0x0) at kernel/qobject.cpp:3113
#11 0xb5c65e42 in QMetaObject::activate (sender=0xc4d6050, m=0xb5d42904, local_signal_index=0, argv=0x0) at kernel/qobject.cpp:3187
#12 0xb5ca1687 in QTimer::timeout (this=0xc4d6050) at .moc/release-shared/moc_qtimer.cpp:128
#13 0xb5c6b5ce in QTimer::timerEvent (this=0xc4d6050, e=0xbfee8cac) at kernel/qtimer.cpp:261
#14 0xb5c6016f in QObject::event (this=0xc4d6050, e=0xbfee8cac) at kernel/qobject.cpp:1075
#15 0xb6112d3c in QApplicationPrivate::notify_helper (this=0x94bd648, receiver=0xc4d6050, e=0xbfee8cac) at kernel/qapplication.cpp:4056
#16 0xb611b03e in QApplication::notify (this=0xbfee8f58, receiver=0xc4d6050, e=0xbfee8cac) at kernel/qapplication.cpp:3603
#17 0xb6d0c85d in KApplication::notify (this=0xbfee8f58, receiver=0xc4d6050, event=0xbfee8cac) at /build/buildd/kde4libs-4.3.1/kdeui/kernel/kapplication.cpp:302
#18 0xb5c4fbcb in QCoreApplication::notifyInternal (this=0xbfee8f58, receiver=0xc4d6050, event=0xbfee8cac) at kernel/qcoreapplication.cpp:610
#19 0xb5c7ed51 in QTimerInfoList::activateTimers (this=0x94b178c) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:213
#20 0xb5c7b3a0 in timerSourceDispatch (source=0x94b1758) at kernel/qeventdispatcher_glib.cpp:165
#21 0xb4d20b88 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#22 0xb4d240eb in ?? () from /usr/lib/libglib-2.0.so.0
#23 0xb4d24268 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#24 0xb5c7b2f8 in QEventDispatcherGlib::processEvents (this=0x9491028, flags={i = -1074885080}) at kernel/qeventdispatcher_glib.cpp:327
#25 0xb61b4a75 in QGuiEventDispatcherGlib::processEvents (this=0x9491028, flags={i = -1074885032}) at kernel/qguieventdispatcher_glib.cpp:202
#26 0xb5c4e1fa in QEventLoop::processEvents (this=0xbfee8ed0, flags={i = -1074884968}) at kernel/qeventloop.cpp:149
#27 0xb5c4e642 in QEventLoop::exec (this=0xbfee8ed0, flags={i = -1074884904}) at kernel/qeventloop.cpp:201
#28 0xb5c50ae9 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:888
#29 0xb6112bb7 in QApplication::exec () at kernel/qapplication.cpp:3525
#30 0x0804bfef in main (argc=3, argv=0xbfee9254) at /build/buildd/kdepim-4.3.1/kontact/src/main.cpp:218

Reported using DrKonqi