kmail crashed whilst downloading emails from a Pop account. Seemingly random, I 
had no other kmail windows open. the download got to about 30% then crashed. On 
restart the emails came though without a problem. 

Sorry not very helpful, but here is the backtrace that might say something:


Application: KMail (kmail), signal SIGSEGV
Using host libthread_db library "/lib/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread -1208281392 (LWP 2994)]
[KCrash handler]
#6  0x0020c1f1 in QUrl (this=0xbfdd06fc, other=@0x51) at io/qurl.cpp:3769
#7  0x0054f502 in KUrl (this=0xbfdd06fc, _u=@0x51)
    at /home/kde-devel/kde/src/kdelibs/kdecore/io/kurl.cpp:431
#8  0x03cccce7 in KIO::SchedulerPrivate::slotScheduleCoSlave (this=0x9b6dcb0)
    at /home/kde-devel/kde/src/kdelibs/kio/kio/scheduler.cpp:883
#9  0x03cd0024 in KIO::Scheduler::qt_metacall (this=0x9b79020, 
    _c=QMetaObject::InvokeMetaMethod, _id=10, _a=0xbfdd07e4)
    at /home/kde-devel/kde/build/kdelibs/kio/scheduler.moc:105
#10 0x0026ae61 in QMetaObject::activate (sender=0x9b6dccc, 
    from_signal_index=4, to_signal_index=4, argv=0x0)
    at kernel/qobject.cpp:3007
#11 0x0026b2e3 in QMetaObject::activate (sender=0x9b6dccc, m=0x305b64, 
    local_signal_index=0, argv=0x0) at kernel/qobject.cpp:3080
#12 0x002ab3bd in QTimer::timeout (this=0x9b6dccc)
    at .moc/debug-shared/moc_qtimer.cpp:126
#13 0x00275f56 in QTimer::timerEvent (this=0x9b6dccc, e=0xbfdd0df4)
    at kernel/qtimer.cpp:263
#14 0x0026a0e2 in QObject::event (this=0x9b6dccc, e=0xbfdd0df4)
    at kernel/qobject.cpp:1105
#15 0x0573ad07 in QApplicationPrivate::notify_helper (this=0x9a34948, 
    receiver=0x9b6dccc, e=0xbfdd0df4) at kernel/qapplication.cpp:3772
#16 0x0573b020 in QApplication::notify (this=0xbfdd110c, receiver=0x9b6dccc, 
    e=0xbfdd0df4) at kernel/qapplication.cpp:3366
#17 0x012e2275 in KApplication::notify (this=0xbfdd110c, receiver=0x9b6dccc, 
    event=0xbfdd0df4)
    at /home/kde-devel/kde/src/kdelibs/kdeui/kernel/kapplication.cpp:311
#18 0x00256bb2 in QCoreApplication::notifyInternal (this=0xbfdd110c, 
    receiver=0x9b6dccc, event=0xbfdd0df4) at kernel/qcoreapplication.cpp:583
#19 0x0025a63b in QCoreApplication::sendEvent (receiver=0x9b6dccc, 
    event=0xbfdd0df4)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:215
#20 0x00289045 in QTimerInfoList::activateTimers (this=0x9a37674)
    at kernel/qeventdispatcher_unix.cpp:563
#21 0x00286164 in timerSourceDispatch (source=0x9a37640)
    at kernel/qeventdispatcher_glib.cpp:166
#22 0x016cf1ac in g_main_context_dispatch () from /lib/libglib-2.0.so.0
#23 0x016d25ef in ?? () from /lib/libglib-2.0.so.0
#24 0x016d2b55 in g_main_context_iteration () from /lib/libglib-2.0.so.0
#25 0x00285be4 in QEventDispatcherGlib::processEvents (this=0x9a31550, 
    flags=@0xbfdd0f68) at kernel/qeventdispatcher_glib.cpp:325
#26 0x057e2db4 in QGuiEventDispatcherGlib::processEvents (this=0x9a31550, 
    flags=@0xbfdd0f98) at kernel/qguieventdispatcher_glib.cpp:204
#27 0x0025370e in QEventLoop::processEvents (this=0xbfdd1010, 
    flags=@0xbfdd0fd4) at kernel/qeventloop.cpp:149
#28 0x0025394d in QEventLoop::exec (this=0xbfdd1010, flags=@0xbfdd1018)
    at kernel/qeventloop.cpp:196
#29 0x0025739b in QCoreApplication::exec () at kernel/qcoreapplication.cpp:845
#30 0x0573aa04 in QApplication::exec () at kernel/qapplication.cpp:3304
#31 0x0804b05c in main (argc=3, argv=0xbfdd11e4)
    at /home/kde-devel/kde/src/kdepim/kmail/main.cpp:146
#0  0x00110402 in __kernel_vsyscall ()