Version:           3.5.5.dfsg.1-6  (using KDE KDE 3.5.5)
Installed from:    Debian testing/unstable Packages
OS:                Linux

I have a rather sticky problem which is there since at least half a year (I'm running with Debian unstable) but I did't come around to report it till now. I got an IMAP Folder configured which has my Spam Mail (about 5k at the moment). Unfortunately I can't access the folder anymore, because when I click on the folder (or go there by pressing the '+' key) KMail blocks for a couple of seconds (screen redrawing isn't done as well) and then silently dies.

I created a backtrace:
#0  0xb7ea325d in (anonymous namespace)::copy_from_stream<unsigned int> () from /usr/lib/libkmailprivate.so
#1  0xb7be37a1 in KMMsgBase::getLongPart () from /usr/lib/libkmailprivate.so
#2  0xb7be3c55 in KMMsgInfo::status () from /usr/lib/libkmailprivate.so
#3  0xb7bb5e71 in KMMsgBase::isDeleted () from /usr/lib/libkmailprivate.so
#4  0xb7d557e9 in KMFolderIndex::readIndex () from /usr/lib/libkmailprivate.so
#5  0xb7da0a0e in KMFolderMbox::open () from /usr/lib/libkmailprivate.so
#6  0xb7e31677 in KMMainWidget::folderSelected () from /usr/lib/libkmailprivate.so
#7  0xb7e318b2 in KMMainWidget::folderSelectedUnread () from /usr/lib/libkmailprivate.so
#8  0xb7e789f0 in KMMainWidget::qt_invoke () from /usr/lib/libkmailprivate.so
#9  0xb70cdd4f in QObject::activate_signal (this=0x88d5230, clist=0x88da510, o=0xbfec4ec4) at kernel/qobject.cpp:2356
#10 0xb7bfb63f in KMFolderTree::folderSelectedUnread () from /usr/lib/libkmailprivate.so
#11 0xb7dc47f2 in KMFolderTree::checkUnreadFolder () from /usr/lib/libkmailprivate.so
#12 0xb7dc49b9 in KMFolderTree::nextUnreadFolder () from /usr/lib/libkmailprivate.so
#13 0xb7dc4ad9 in KMMainWidget::slotNextUnreadMessage () from /usr/lib/libkmailprivate.so
#14 0xb7e793f0 in KMMainWidget::qt_invoke () from /usr/lib/libkmailprivate.so
#15 0xb70cdd4f in QObject::activate_signal (this=0x8908ed0, clist=0x8909108, o=0xbfec50ac) at kernel/qobject.cpp:2356
#16 0xb70ce7e0 in QObject::activate_signal (this=0x8908ed0, signal=2) at kernel/qobject.cpp:2325
#17 0xb5e7b259 in KAction::activated (this=0x8908ed0) at ./kaction.moc:176
#18 0xb5eb0971 in KAction::slotActivated (this=0x8908ed0) at /home/ana/Debian/kdelibs/kdelibs-3.5.5a.dfsg.1/./kdeui/kaction.cpp:1102
#19 0xb5f90faf in KAction::qt_invoke (this=0xbfec50ac, _id=15, _o=0xbfec51bc) at ./kaction.moc:218
#20 0xb70cdd4f in QObject::activate_signal (this=0x89d6850, clist=0x89ef9b8, o=0xbfec51bc) at kernel/qobject.cpp:2356
#21 0xb70ce7e0 in QObject::activate_signal (this=0x89d6850, signal=2) at kernel/qobject.cpp:2325
#22 0xb76a39c9 in KAccelPrivate::menuItemActivated (this=0x89d6850) at ./kaccelprivate.moc:110
#23 0xb76f36b7 in KAccelPrivate::emitActivatedSignal (this=0x89d6850, pAction=0x8a0c6f0) at /home/ana/Debian/kdelibs/kdelibs-3.5.5a.dfsg.1/./kdecore/kaccel.cpp:403
#24 0xb777e4bc in KAccelPrivate::eventFilter (this=0x89d6850, pEvent=0xbfec568c) at /home/ana/Debian/kdelibs/kdelibs-3.5.5a.dfsg.1/./kdecore/kaccel.cpp:373
#25 0xb70cd302 in QObject::activate_filters (this=0x8822810, e=0xbfec568c) at kernel/qobject.cpp:903
#26 0xb70cd380 in QObject::event (this=0x8822810, e=0xbfec568c) at kernel/qobject.cpp:735
#27 0xb7104612 in QWidget::event (this=0x8822810, e=0xbfec568c) at kernel/qwidget.cpp:4678
#28 0xb71d98bc in QMainWindow::event (this=0x8822810, e=0xbfec568c) at widgets/qmainwindow.cpp:1687
#29 0xb7065c26 in QApplication::internalNotify (this=0xbfec5b44, receiver=0x8822810, e=0xbfec568c) at kernel/qapplication.cpp:2635
#30 0xb7067bda in QApplication::notify (this=0xbfec5b44, receiver=0x88d5230, e=0xbfec568c) at kernel/qapplication.cpp:2392
#31 0xb778de0e in KApplication::notify (this=0xbfec5b44, receiver=0x88d5230, event=0xbfec568c)
    at /home/ana/Debian/kdelibs/kdelibs-3.5.5a.dfsg.1/./kdecore/kapplication.cpp:550
#32 0xb76ffbc7 in KAccelEventHandler::x11Event (this=0x88279e8, pEvent=0xbfec59b8) at /usr/share/qt3/include/qapplication.h:520
#33 0xb7784c03 in KApplication::x11EventFilter (this=0xbfec5b44, _event=0xbfec59b8) at /home/ana/Debian/kdelibs/kdelibs-3.5.5a.dfsg.1/./kdecore/kapplication.cpp:1651
#34 0xb6fe6183 in qt_x11EventFilter (ev=0xbfec59b8) at kernel/qapplication_x11.cpp:387
#35 0xb6ff60ab in QApplication::x11ProcessEvent (this=0xbfec5b44, event=0xbfec59b8) at kernel/qapplication_x11.cpp:3343
#36 0xb700cd02 in QEventLoop::processEvents (this=0x80863e0, flags=4) at kernel/qeventloop_x11.cpp:192
#37 0xb7080179 in QEventLoop::enterLoop (this=0x80863e0) at kernel/qeventloop.cpp:198
#38 0xb707ff9a in QEventLoop::exec (this=0x80863e0) at kernel/qeventloop.cpp:145
#39 0xb70677bf in QApplication::exec (this=0xbfec5b44) at kernel/qapplication.cpp:2758
#40 0x0804a094 in ?? ()
#41 0xbfec5b44 in ?? ()
#42 0xbfec5d30 in ?? ()
#43 0x00000000 in ?? ()

Hope this help. I am able to use a compiler and am willing to test patches.