Version:           1.10.1 (using KDE 4.1.1)
OS:                Linux
Installed from:    Ubuntu Packages

Kmail crashed every time I select the body part of the E-mail. Using the anti-spam wizard, I set up both bogoff filter and spamassassin. Removing all spam filters rectified the problem. Currently only using spamassassin without any problems.
Backtrace:

Application: KMail (kmail), signal SIGABRT
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
[Thread debugging using libthread_db enabled]
[New Thread 0xb4388720 (LWP 23419)]
[KCrash handler]
#6  0xb7ef0410 in __kernel_vsyscall ()
#7  0xb657a085 in raise () from /lib/tls/i686/cmov/libc.so.6
#8  0xb657ba01 in abort () from /lib/tls/i686/cmov/libc.so.6
#9  0xb711c367 in qt_message_output (msgType=QtFatalMsg, 
    buf=0xbfcc04dc "ASSERT: \"dict\" in file /build/buildd/kde4libs-4.1.1+really4.1.1/kdecore/sonnet/loader.cpp, line 116") at global/qglobal.cpp:2061
#10 0xb711c458 in qFatal (msg=0xb7263498 "ASSERT: \"%s\" in file %s, line %d")
    at global/qglobal.cpp:2263
#11 0xb711c505 in qt_assert (assertion=0xb74de041 "dict", 
    file=0xb74dde40 "/build/buildd/kde4libs-4.1.1+really4.1.1/kdecore/sonnet/loader.cpp", line=116) at global/qglobal.cpp:1831
#12 0xb74428d2 in Sonnet::Loader::createSpeller (this=0x85555a0, 
    language=@0x88e9b40, clientName=@0xbfcc2598)
    at /build/buildd/kde4libs-4.1.1+really4.1.1/kdecore/sonnet/loader.cpp:116
#13 0xb7444dae in Sonnet::Speller::Private::recreateDict (this=0x88e9b38)
    at /build/buildd/kde4libs-4.1.1+really4.1.1/kdecore/sonnet/speller.cpp:63
#14 0xb770181f in Sonnet::Highlighter::setCurrentLanguage (this=0x885fd28, 
    lang=@0x87d61d4)
    at /build/buildd/kde4libs-4.1.1+really4.1.1/kdeui/sonnet/highlighter.cpp:296
#15 0xb78fa990 in KPIM::KMeditor::setSpellCheckLanguage ()
   from /usr/lib/kde4/lib/libkdepim.so.4
#16 0xb78fc996 in KPIM::KMeditor::createHighlighter ()
   from /usr/lib/kde4/lib/libkdepim.so.4
#17 0xb7787881 in KTextEdit::focusInEvent (this=0x87d2ea8, event=0xbfcc2c48)
    at /build/buildd/kde4libs-4.1.1+really4.1.1/kdeui/widgets/ktextedit.cpp:463
#18 0xb692eb34 in QWidget::event (this=0x87d2ea8, event=0xbfcc2c48)
    at kernel/qwidget.cpp:7119
#19 0xb6c692a3 in QFrame::event (this=0x87d2ea8, e=0xbfcc2c48)
    at widgets/qframe.cpp:657
#20 0xb6cfd815 in QAbstractScrollArea::event (this=0x87d2ea8, e=0xbfcc2c48)
    at widgets/qabstractscrollarea.cpp:903
#21 0xb6ce6c72 in QTextEdit::event (this=0x87d2ea8, e=0xbfcc2c48)
    at widgets/qtextedit.cpp:1055
#22 0xb7788949 in KTextEdit::event (this=0x87d2ea8, ev=0xbfcc2c48)
    at /build/buildd/kde4libs-4.1.1+really4.1.1/kdeui/widgets/ktextedit.cpp:241
#23 0xb68d6f9c in QApplicationPrivate::notify_helper (this=0x806a4d8, 
    receiver=0x87d2ea8, e=0xbfcc2c48) at kernel/qapplication.cpp:3800
#24 0xb68dbce8 in QApplication::notify (this=0xbfcc3ca8, receiver=0x87d2ea8, 
    e=0xbfcc2c48) at kernel/qapplication.cpp:3765
#25 0xb76a71c3 in KApplication::notify (this=0xbfcc3ca8, receiver=0x87d2ea8, 
    event=0xbfcc2c48)
    at /build/buildd/kde4libs-4.1.1+really4.1.1/kdeui/kernel/kapplication.cpp:311
#26 0xb72100b9 in QCoreApplication::notifyInternal (this=0xbfcc3ca8, 
    receiver=0x87d2ea8, event=0xbfcc2c48) at kernel/qcoreapplication.cpp:591
#27 0xb68d9c0c in QApplicationPrivate::setFocusWidget (focus=0x87d2ea8, 
    reason=Qt::TabFocusReason)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:215
#28 0xb692515e in QWidget::setFocus (this=0x87d2ea8, 
    reason=Qt::TabFocusReason) at kernel/qwidget.cpp:5241
#29 0xb6925473 in QWidget::focusNextPrevChild (this=0x854cf58, next=true)
    at kernel/qwidget.cpp:5380
#30 0xb692543f in QWidget::focusNextPrevChild (this=0x854f610, next=6)
    at kernel/qwidget.cpp:5375
#31 0xb692543f in QWidget::focusNextPrevChild (this=0x854edb0, next=6)
    at kernel/qwidget.cpp:5375
#32 0xb692543f in QWidget::focusNextPrevChild (this=0x83ede20, next=6)
    at kernel/qwidget.cpp:5375
#33 0xb692543f in QWidget::focusNextPrevChild (this=0x87cfd18, next=6)
    at kernel/qwidget.cpp:5375
#34 0xb692f2d5 in QWidget::event (this=0x87cfd18, event=0xbfcc3294)
    at kernel/qwidget.cpp:7052
#35 0xb6c7f34f in QLineEdit::event (this=0x87cfd18, e=0xbfcc3294)
    at widgets/qlineedit.cpp:1602
#36 0xb775694a in KLineEdit::event (this=0x87cfd18, ev=0xbfcc3294)
    at /build/buildd/kde4libs-4.1.1+really4.1.1/kdeui/widgets/klineedit.cpp:1296
#37 0xb68d6f9c in QApplicationPrivate::notify_helper (this=0x806a4d8, 
    receiver=0x87cfd18, e=0xbfcc3294) at kernel/qapplication.cpp:3800
#38 0xb68dbf3c in QApplication::notify (this=0xbfcc3ca8, receiver=0x87cfd18, 
    e=0xbfcc3294) at kernel/qapplication.cpp:3446
#39 0xb76a71c3 in KApplication::notify (this=0xbfcc3ca8, receiver=0x87cfd18, 
    event=0xbfcc3294)
    at /build/buildd/kde4libs-4.1.1+really4.1.1/kdeui/kernel/kapplication.cpp:311
#40 0xb72100b9 in QCoreApplication::notifyInternal (this=0xbfcc3ca8, 
    receiver=0x87cfd18, event=0xbfcc3294) at kernel/qcoreapplication.cpp:591
#41 0xb6932a5e in qt_sendSpontaneousEvent (receiver=0x87cfd18, 
    event=0xbfcc3294)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:218
#42 0xb696775b in QKeyMapper::sendKeyEvent (keyWidget=0x87cfd18, grab=false, 
    type=QEvent::KeyPress, code=16777217, modifiers=@0xbfcc3400, 
    text=@0xbfcc3434, autorepeat=<value optimized out>, count=1, 
    nativeScanCode=23, nativeVirtualKey=65289, nativeModifiers=0)
    at kernel/qkeymapper_x11.cpp:1658
#43 0xb696983e in QKeyMapperPrivate::translateKeyEvent (this=0x808d608, 
    keyWidget=0x87cfd18, event=0xbfcc3968, grab=<value optimized out>)
    at kernel/qkeymapper_x11.cpp:1629
#44 0xb6941d15 in QApplication::x11ProcessEvent (this=0xbfcc3ca8, 
    event=0xbfcc3968) at kernel/qapplication_x11.cpp:3059
#45 0xb696ac2a in x11EventSourceDispatch (s=0x806d398, callback=0, 
    user_data=0x0) at kernel/qguieventdispatcher_glib.cpp:148
#46 0xb4ceadd6 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#47 0xb4cee193 in ?? () from /usr/lib/libglib-2.0.so.0
#48 0xb4cee74e in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#49 0xb723b9f8 in QEventDispatcherGlib::processEvents (this=0x8067218, 
    flags=@0xbfcc3b08) at kernel/qeventdispatcher_glib.cpp:325
#50 0xb696aa25 in QGuiEventDispatcherGlib::processEvents (this=0x8067218, 
    flags=@0xbfcc3b38) at kernel/qguieventdispatcher_glib.cpp:204
#51 0xb720f33d in QEventLoop::processEvents (this=0xbfcc3bb0, 
    flags=@0xbfcc3b74) at kernel/qeventloop.cpp:149
#52 0xb720f4cd in QEventLoop::exec (this=0xbfcc3bb0, flags=@0xbfcc3bb8)
    at kernel/qeventloop.cpp:200
#53 0xb721174d in QCoreApplication::exec () at kernel/qcoreapplication.cpp:849
#54 0xb68d6897 in QApplication::exec () at kernel/qapplication.cpp:3330
#55 0x0804a85f in _start ()
#0  0xb7ef0410 in __kernel_vsyscall ()