Version:           1.9.51 (using 4.00.82 (KDE 4.0.82 >= 20080610), Debian packages)
Compiler:          cc
OS:                Linux (x86_64) release 2.6.25-melech

While KMail was applying filters to some 40 new messages in an IMAP mailbox (with the status bar showing the countdown of messages left to filter), I opened the filter settings and deleted the filter (the only one I had configured). KMail crashed immediately afterwards.

Program: KMail (kmail), signal SIGSEGV
[Thread debugging using libthread_db enabled]
[New Thread 0x7f7009490780 (LWP 28330)]
[New Thread 0x415e5950 (LWP 28695)]
[KCrash handler]
#5  KMSearchPattern::matches (this=0x8a6cf0, serNum=37780, ignoreBody=false)
    at /tmp/buildd/kdepim-4.0.82+svn819867/kmail/kmsearchpattern.cpp:774
#6  0x00007f7008c6549c in KMail::ActionScheduler::filterMessage (
    this=0xcd5f60)
    at /tmp/buildd/kdepim-4.0.82+svn819867/kmail/actionscheduler.cpp:619
#7  0x00007f7008c655ea in KMail::ActionScheduler::qt_metacall (this=0xcd5f60, 
    _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, 
    _a=0x7fff115d8e50)
    at /tmp/buildd/kdepim-4.0.82+svn819867/obj-x86_64-linux-gnu/kmail/actionscheduler.moc:123
#8  0x00007f70079c97e4 in QMetaObject::activate (sender=0xcd23c0, 
    from_signal_index=<value optimized out>, to_signal_index=4, 
    argv=0x1752478) at kernel/qobject.cpp:3010
#9  0x00007f70079c40f3 in QObject::event (this=0xcd23c0, e=0x9394)
    at kernel/qobject.cpp:1105
#10 0x00007f7006ee3e5d in QApplicationPrivate::notify_helper (this=0x62ef10, 
    receiver=0xcd23c0, e=0x7fff115d9510) at kernel/qapplication.cpp:3772
#11 0x00007f7006eebb2a in QApplication::notify (this=0x7fff115d9950, 
    receiver=0xcd23c0, e=0x7fff115d9510) at kernel/qapplication.cpp:3739
#12 0x00007f7008314e5b in KApplication::notify (this=0x7fff115d9950, 
    receiver=0xcd23c0, event=0x7fff115d9510)
    at /tmp/buildd/kde4libs-4.0.82+svn819867/kdeui/kernel/kapplication.cpp:311
#13 0x00007f70079b5491 in QCoreApplication::notifyInternal (
    this=0x7fff115d9950, receiver=0xcd23c0, event=0x7fff115d9510)
    at kernel/qcoreapplication.cpp:587
#14 0x00007f70079e1436 in QTimerInfoList::activateTimers (this=0x6326d0)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:215
#15 0x00007f70079dd95d in timerSourceDispatch (source=<value optimized out>)
    at kernel/qeventdispatcher_glib.cpp:166
#16 0x00007f6fff28c0f2 in g_main_context_dispatch ()
   from /usr/lib/libglib-2.0.so.0
#17 0x00007f6fff28f396 in ?? () from /usr/lib/libglib-2.0.so.0
#18 0x00007f6fff28f82f in g_main_context_iteration ()
   from /usr/lib/libglib-2.0.so.0
#19 0x00007f70079dd8bf in QEventDispatcherGlib::processEvents (this=0x620c80, 
    flags=<value optimized out>) at kernel/qeventdispatcher_glib.cpp:325
#20 0x00007f7006f7516f in QGuiEventDispatcherGlib::processEvents (
    this=0x8a6cf0, flags=<value optimized out>)
    at kernel/qguieventdispatcher_glib.cpp:204
#21 0x00007f70079b3da2 in QEventLoop::processEvents (
    this=<value optimized out>, flags={i = 291346272})
    at kernel/qeventloop.cpp:149
#22 0x00007f70079b3f2d in QEventLoop::exec (this=0x7fff115d97a0, flags=
      {i = 291346352}) at kernel/qeventloop.cpp:200
#23 0x00007f70079b63fd in QCoreApplication::exec ()
    at kernel/qcoreapplication.cpp:845
#24 0x0000000000402f14 in main (argc=<value optimized out>, 
    argv=<value optimized out>)
    at /tmp/buildd/kdepim-4.0.82+svn819867/kmail/main.cpp:130
#0  0x00007f7006548241 in nanosleep () from /lib/libc.so.6