Version:           1.9.5 (using KDE KDE 3.5.5)
Installed from:    Debian testing/unstable Packages
OS:                Linux

I enabled the Bogofilter and spam assassin anti-spam software. Then I selected about 20 emails and pressed the button to mark those messages as not-spam. Then it crashed and I got a trace:

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Using host libthread_db library "/lib/i686/cmov/libthread_db.so.1".
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[Thread debugging using libthread_db enabled]
[New Thread -1249311024 (LWP 2533)]
[New Thread -1281700976 (LWP 2570)]
[New Thread -1273308272 (LWP 2569)]
[New Thread -1264915568 (LWP 2568)]
[New Thread -1256522864 (LWP 2567)]
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[KCrash handler]
#9  0xb73ada29 in QGList::append () from /usr/lib/libqt-mt.so.3
#10 0xb70548d0 in QPtrList<QPostEvent>::append () from /usr/lib/libqt-mt.so.3
#11 0xb704d2a8 in QApplication::postEvent () from /usr/lib/libqt-mt.so.3
#12 0xb70b491e in QObject::deleteLater () from /usr/lib/libqt-mt.so.3
#13 0xb5b171e4 in KIO::Job::emitResult () from /usr/lib/libkio.so.4
#14 0xb5b17592 in KIO::Job::removeSubjob () from /usr/lib/libkio.so.4
#15 0xb5b17673 in KIO::Job::removeSubjob () from /usr/lib/libkio.so.4
#16 0xb5ad2d7a in KIO::Job::slotResult () from /usr/lib/libkio.so.4
#17 0xb7bdee1e in KMMessage::setTransferInProgress ()
   from /usr/lib/libkmailprivate.so
#18 0xb7bec4e0 in KMCommand::slotPostTransfer ()
   from /usr/lib/libkmailprivate.so
#19 0xb7c78126 in KMCommand::qt_invoke () from /usr/lib/libkmailprivate.so
#20 0xb7c7872b in KMFilterActionCommand::qt_invoke ()
   from /usr/lib/libkmailprivate.so
#21 0xb70b3d4f in QObject::activate_signal () from /usr/lib/libqt-mt.so.3
#22 0xb7bec66e in KMCommand::messagesTransfered ()
   from /usr/lib/libkmailprivate.so
#23 0xb7c7803d in KMCommand::slotJobFinished ()
   from /usr/lib/libkmailprivate.so
#24 0xb7c780f2 in KMCommand::qt_invoke () from /usr/lib/libkmailprivate.so
#25 0xb7c7872b in KMFilterActionCommand::qt_invoke ()
   from /usr/lib/libkmailprivate.so
#26 0xb70b3d4f in QObject::activate_signal () from /usr/lib/libqt-mt.so.3
#27 0xb70b47e0 in QObject::activate_signal () from /usr/lib/libqt-mt.so.3
#28 0xb7bcfc2c in KMail::FolderJob::finished ()
   from /usr/lib/libkmailprivate.so
#29 0xb7c70438 in KMail::FolderJob::~FolderJob ()
   from /usr/lib/libkmailprivate.so
#30 0xb7d55075 in KMail::ImapJob::~ImapJob () from /usr/lib/libkmailprivate.so
#31 0xb70b341e in QObject::event () from /usr/lib/libqt-mt.so.3
#32 0xb704bc26 in QApplication::internalNotify () from /usr/lib/libqt-mt.so.3
#33 0xb704da43 in QApplication::notify () from /usr/lib/libqt-mt.so.3
#34 0xb7774e0e in KApplication::notify () from /usr/lib/libkdecore.so.4
#35 0xb6fdf421 in QApplication::sendEvent () from /usr/lib/libqt-mt.so.3
#36 0xb704cc4e in QApplication::sendPostedEvents ()
   from /usr/lib/libqt-mt.so.3
#37 0xb704cd56 in QApplication::sendPostedEvents ()
   from /usr/lib/libqt-mt.so.3
#38 0xb6ff2c55 in QEventLoop::processEvents () from /usr/lib/libqt-mt.so.3
#39 0xb7066179 in QEventLoop::enterLoop () from /usr/lib/libqt-mt.so.3
#40 0xb7065f9a in QEventLoop::exec () from /usr/lib/libqt-mt.so.3
#41 0xb704d7bf in QApplication::exec () from /usr/lib/libqt-mt.so.3
#42 0x0804a094 in ?? ()
#43 0xbfdc2d74 in ?? ()
#44 0xbfdc2f60 in ?? ()
#45 0x00000000 in ?? ()

This is the only information I have about it.