Version:            (using KDE Devel)
Installed from:    Compiled sources
Compiler:          gcc 3.3.4 
OS:                Linux

Using shift+Delete to remove some unneeded messages from one of my folders caused kmail to crash with the following backtrace.

Using host libthread_db library "/lib/libthread_db.so.1".
[KCrash handler]
#34 0x00000000 in ?? ()
#35 0x4036f95c in KMMoveCommand::execute () at certificatewizard.cpp:33
#36 0x40367014 in KMCommand::slotPostTransfer () at certificatewizard.cpp:33
#37 0x40360d98 in KMCommand::qt_invoke () at certificatewizard.cpp:33
#38 0x403646b4 in KMMenuCommand::qt_invoke () at certificatewizard.cpp:33
#39 0x40364a63 in KMMoveCommand::qt_invoke () at certificatewizard.cpp:33
#40 0x41c843bb in QObject::activate_signal (this=0x81a3fd0, clist=0x8312e68, 
    o=0xbfffeb10) at kernel/qobject.cpp:2357
#41 0x40360c27 in KMCommand::messagesTransfered () at certificatewizard.cpp:33
#42 0x4036735a in KMCommand::transferSelectedMsgs ()
    at certificatewizard.cpp:33
#43 0x40366e42 in KMCommand::slotStart () at certificatewizard.cpp:33
#44 0x40360d84 in KMCommand::qt_invoke () at certificatewizard.cpp:33
#45 0x403646b4 in KMMenuCommand::qt_invoke () at certificatewizard.cpp:33
#46 0x40364a63 in KMMoveCommand::qt_invoke () at certificatewizard.cpp:33
#47 0x41c843bb in QObject::activate_signal (this=0x824d3f8, clist=0x82fdf08, 
    o=0xbfffed80) at kernel/qobject.cpp:2357
#48 0x41fdd59c in QSignal::signal (this=0x824d3f8, t0=@0x824d420)
    at .moc/debug-shared-mt/moc_qsignal.cpp:100
#49 0x41ca1b87 in QSignal::activate (this=0x824d3f8) at kernel/qsignal.cpp:212
#50 0x41ca90bb in QSingleShotTimer::event (this=0x824d3d0)
    at kernel/qtimer.cpp:277
#51 0x41c212a7 in QApplication::internalNotify (this=0xbffff3d0, 
    receiver=0x824d3d0, e=0xbffff060) at kernel/qapplication.cpp:2635
#52 0x41c20764 in QApplication::notify (this=0xbffff3d0, receiver=0x824d3d0, 
    e=0xbffff060) at kernel/qapplication.cpp:2358
#53 0x41757ceb in KApplication::notify (this=0xbffff3d0, receiver=0x824d3d0, 
    event=0xbffff060)
    at /home/gdcb04/src/kde/kdelibs/kdecore/kapplication.cpp:516
#54 0x41bb6dfd in QApplication::sendEvent (receiver=0x824d3d0, 
    event=0xbffff060) at qapplication.h:491
#55 0x41c0f3ce in QEventLoop::activateTimers (this=0x808dcc0)
    at kernel/qeventloop_unix.cpp:558
#56 0x41bc8a19 in QEventLoop::processEvents (this=0x808dcc0, flags=4)
    at kernel/qeventloop_x11.cpp:389
#57 0x41c35616 in QEventLoop::enterLoop (this=0x808dcc0)
    at kernel/qeventloop.cpp:198
#58 0x41c35532 in QEventLoop::exec (this=0x808dcc0)
    at kernel/qeventloop.cpp:145
#59 0x41c21427 in QApplication::exec (this=0xbffff3d0)
    at kernel/qapplication.cpp:2758
#60 0x0804a73c in main ()

I've so far been able to reproduce this two times.