Version:           4.1.0 (using KDE 4.1.0)
Installed from:    Debian testing/unstable Packages
Compiler:          gcc (Debian 4.3.1-8) 4.3.1 
OS:                Linux

It's pretty easy to reproduce this one, just use KMail for longer than 5 minutes on an IMAP server. Part of the problem might be that I'm using a server 1 hop from this machine, so it's very responsive. This may trigger race conditions that more remote IMAP servers wouldn't.

Application: KMail (kmail), signal SIGSEGV
[Thread debugging using libthread_db enabled]
[New Thread 0x7f79dc55c780 (LWP 6383)]
[KCrash handler]
#5  0x00007f79dbe414d5 in KMail::ISubject::notify (this=0x3f4b238)
    at /tmp/buildd/kdepim-4.1.0/kmail/isubject.cpp:30
#6  0x00007f79dbaf40ac in KMMessage::updateBodyPart (this=0x3f4b210, 
    partSpecifier=
      {static null = {<No data fields>}, static shared_null = {ref = {_q_value = 13567}, alloc = 0, size = 0, data = 0x7f79dac5883a, clean = 0, simpletext = 0, righttoleft = 0, asciiCache = 0, capacity = 0, reserved = 0, array = {0}}, static shared_empty = {ref = {_q_value = 555}, alloc = 0, size = 0, data = 0x7f79dac5885a, clean = 0, simpletext = 0, righttoleft = 0, asciiCache = 0, capacity = 0, reserved = 0, array = {0}}, d = 0x7fffe45a04f0, static codecForCStrings = 0x0}, data=<value optimized out>)
    at /tmp/buildd/kdepim-4.1.0/kmail/kmmessage.cpp:4178
#7  0x00007f79dbe19603 in KMail::ImapJob::slotGetMessageResult (
    this=0x1334870, job=0x1e7d9b0)
    at /tmp/buildd/kdepim-4.1.0/kmail/imapjob.cpp:435
#8  0x00007f79dbe1a4e7 in KMail::ImapJob::qt_metacall (this=0x1334870, 
    _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, 
    _a=0x7fffe45a0680)
    at /tmp/buildd/kdepim-4.1.0/obj-x86_64-linux-gnu/kmail/imapjob.moc:81
#9  0x00007f79da985764 in QMetaObject::activate (sender=0x1e7d9b0, 
    from_signal_index=<value optimized out>, to_signal_index=7, 
    argv=0x3f187f0) at kernel/qobject.cpp:3010
#10 0x00007f79dad4ebc2 in KJob::result (this=0x1158be8, _t1=0x1e7d9b0)
    at /tmp/buildd/kde4libs-4.1.0/obj-x86_64-linux-gnu/kdecore/kjob.moc:186
#11 0x00007f79dad4ef87 in KJob::emitResult (this=0x1e7d9b0)
    at /tmp/buildd/kde4libs-4.1.0/kdecore/jobs/kjob.cpp:290
#12 0x00007f79d540fbe0 in KIO::SimpleJob::slotFinished (this=0x1e7d9b0)
    at /tmp/buildd/kde4libs-4.1.0/kio/kio/job.cpp:498
#13 0x00007f79d5416413 in KIO::TransferJob::slotFinished (this=0x1e7d9b0)
    at /tmp/buildd/kde4libs-4.1.0/kio/kio/job.cpp:967
#14 0x00007f79d5417175 in KIO::TransferJob::qt_metacall (this=0x1e7d9b0, 
    _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, 
    _a=0x7fffe45a0a80)
    at /tmp/buildd/kde4libs-4.1.0/obj-x86_64-linux-gnu/kio/jobclasses.moc:336
#15 0x00007f79da985764 in QMetaObject::activate (sender=0x12be790, 
    from_signal_index=<value optimized out>, to_signal_index=8, 
    argv=0x3f187f0) at kernel/qobject.cpp:3010
#16 0x00007f79d54ca1b1 in KIO::SlaveInterface::dispatch (this=0x12be790, 
    _cmd=104, rawdata=<value optimized out>)
    at /tmp/buildd/kde4libs-4.1.0/kio/kio/slaveinterface.cpp:175
#17 0x00007f79d54c7012 in KIO::SlaveInterface::dispatch (this=0x12be790)
    at /tmp/buildd/kde4libs-4.1.0/kio/kio/slaveinterface.cpp:90
#18 0x00007f79d54b8033 in KIO::Slave::gotInput (this=0x12be790)
    at /tmp/buildd/kde4libs-4.1.0/kio/kio/slave.cpp:319
#19 0x00007f79d54ba758 in KIO::Slave::qt_metacall (this=0x12be790, 
    _c=QMetaObject::InvokeMetaMethod, _id=0, _a=0x7fffe45a0ea0)
    at /tmp/buildd/kde4libs-4.1.0/obj-x86_64-linux-gnu/kio/slave.moc:75
#20 0x00007f79da985764 in QMetaObject::activate (sender=0x12d0990, 
    from_signal_index=<value optimized out>, to_signal_index=4, 
    argv=0x3f187f0) at kernel/qobject.cpp:3010
#21 0x00007f79d53dd680 in KIO::ConnectionPrivate::dequeue (this=0x12cff00)
    at /tmp/buildd/kde4libs-4.1.0/kio/kio/connection.cpp:82
#22 0x00007f79d53dd7ba in KIO::Connection::qt_metacall (this=0x12d0990, 
    _c=QMetaObject::InvokeMetaMethod, _id=0, _a=0x1e6d6b0)
    at /tmp/buildd/kde4libs-4.1.0/obj-x86_64-linux-gnu/kio/connection.moc:72
#23 0x00007f79da98040d in QObject::event (this=0x12d0990, e=0x1269d30)
    at kernel/qobject.cpp:1140
#24 0x00007f79d9e9fe5d in QApplicationPrivate::notify_helper (this=0xc48c20, 
    receiver=0x12d0990, e=0x1269d30) at kernel/qapplication.cpp:3772
#25 0x00007f79d9ea7b2a in QApplication::notify (this=0x7fffe45a1a20, 
    receiver=0x12d0990, e=0x1269d30) at kernel/qapplication.cpp:3739
#26 0x00007f79db2cbbfb in KApplication::notify (this=0x7fffe45a1a20, 
    receiver=0x12d0990, event=0x1269d30)
    at /tmp/buildd/kde4libs-4.1.0/kdeui/kernel/kapplication.cpp:311
#27 0x00007f79da971411 in QCoreApplication::notifyInternal (
    this=0x7fffe45a1a20, receiver=0x12d0990, event=0x1269d30)
    at kernel/qcoreapplication.cpp:587
#28 0x00007f79da9720ba in QCoreApplicationPrivate::sendPostedEvents (
    receiver=0x0, event_type=0, data=0xc237e0)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:215
#29 0x00007f79da999bb3 in postEventSourceDispatch (s=<value optimized out>)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:220
#30 0x00007f79d3250c52 in g_main_context_dispatch ()
   from /usr/lib/libglib-2.0.so.0
#31 0x00007f79d32543dd in ?? () from /usr/lib/libglib-2.0.so.0
#32 0x00007f79d325459b in g_main_context_iteration ()
   from /usr/lib/libglib-2.0.so.0
#33 0x00007f79da99983f in QEventDispatcherGlib::processEvents (this=0xc3b5b0, 
    flags=<value optimized out>) at kernel/qeventdispatcher_glib.cpp:325
#34 0x00007f79d9f3116f in QGuiEventDispatcherGlib::processEvents (
    this=0x1158be8, flags=<value optimized out>)
    at kernel/qguieventdispatcher_glib.cpp:204
#35 0x00007f79da96fd22 in QEventLoop::processEvents (
    this=<value optimized out>, flags={i = -463857616})
    at kernel/qeventloop.cpp:149
#36 0x00007f79da96fead in QEventLoop::exec (this=0x7fffe45a1870, flags=
      {i = -463857536}) at kernel/qeventloop.cpp:200
#37 0x00007f79da97237d in QCoreApplication::exec ()
    at kernel/qcoreapplication.cpp:845
#38 0x0000000000402f8b in main (argc=<value optimized out>, 
    argv=<value optimized out>) at /tmp/buildd/kdepim-4.1.0/kmail/main.cpp:146
#0  0x00007f79d95000b0 in __nanosleep_nocancel () from /lib/libc.so.6