Version:            (using KDE 4.2.2)
Installed from:    Ubuntu Packages

Was replying to an email in Thunderbird. When Send button was clicked, window normally disappeared and plasma crashed at this time.

Just supposition: it crashed while animating window fade out. It looked like so.

Find backtrace (french) below:

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Application : Espace de travail Plasma (plasma), signal SIGSEGV
[Current thread is 0 (LWP 4155)]

Thread 3 (Thread 0xa8221b90 (LWP 4156)):
#0  0xb7efa430 in __kernel_vsyscall ()
#1  0xb50360e5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb62452ed in pthread_cond_wait () from /lib/tls/i686/cmov/libc.so.6
#3  0xb64319b2 in QWaitCondition::wait () from /usr/lib/libQtCore.so.4
#4  0xb78b2152 in ?? () from /usr/lib/libQtNetwork.so.4
#5  0xb643096e in ?? () from /usr/lib/libQtCore.so.4
#6  0xb50324ff in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#7  0xb623649e in clone () from /lib/tls/i686/cmov/libc.so.6

Thread 2 (Thread 0xa79d8b90 (LWP 4157)):
#0  0xb7efa430 in __kernel_vsyscall ()
#1  0xb50360e5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb62452ed in pthread_cond_wait () from /lib/tls/i686/cmov/libc.so.6
#3  0xb64319b2 in QWaitCondition::wait () from /usr/lib/libQtCore.so.4
#4  0xa8466b9a in ?? () from /usr/lib/kde4/plasma_wallpaper_image.so
#5  0xb643096e in ?? () from /usr/lib/libQtCore.so.4
#6  0xb50324ff in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#7  0xb623649e in clone () from /lib/tls/i686/cmov/libc.so.6

Thread 1 (Thread 0xb3c1c730 (LWP 4155)):
[KCrash Handler]
#6  0xb653b951 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#7  0xa86270d3 in TaskManager::AbstractGroupingStrategy::groupRemoved () from /usr/lib/libtaskmanager.so.4
#8  0xa86287d1 in TaskManager::AbstractGroupingStrategy::closeGroup () from /usr/lib/libtaskmanager.so.4
#9  0xa862f597 in ?? () from /usr/lib/libtaskmanager.so.4
#10 0xa863023b in ?? () from /usr/lib/libtaskmanager.so.4
#11 0xb653aca8 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#12 0xb653b932 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#13 0xa8641a63 in TaskManager::TaskGroup::itemRemoved () from /usr/lib/libtaskmanager.so.4
#14 0xa86420b0 in TaskManager::TaskGroup::remove () from /usr/lib/libtaskmanager.so.4
#15 0xa862af10 in TaskManager::GroupManager::remove () from /usr/lib/libtaskmanager.so.4
#16 0xa862cc47 in TaskManager::GroupManager::qt_metacall () from /usr/lib/libtaskmanager.so.4
#17 0xb653aca8 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#18 0xb653b932 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#19 0xa8645483 in TaskManager::TaskManager::taskRemoved () from /usr/lib/libtaskmanager.so.4
#20 0xa8646baf in TaskManager::TaskManager::windowRemoved () from /usr/lib/libtaskmanager.so.4
#21 0xa8648a14 in TaskManager::TaskManager::qt_metacall () from /usr/lib/libtaskmanager.so.4
#22 0xb653aca8 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#23 0xb653b932 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#24 0xb7773473 in KWindowSystem::windowRemoved () from /usr/lib/libkdeui.so.5
#25 0xb7775cf6 in ?? () from /usr/lib/libkdeui.so.5
#26 0xb77851d3 in NETRootInfo::update () from /usr/lib/libkdeui.so.5
#27 0xb77855bf in NETRootInfo::event () from /usr/lib/libkdeui.so.5
#28 0xb7775f8d in ?? () from /usr/lib/libkdeui.so.5
#29 0xb7628c69 in KApplication::x11EventFilter () from /usr/lib/libkdeui.so.5
#30 0xb7eb14d7 in ?? () from /usr/lib/libkdeinit4_plasma.so
#31 0xb6834f3e in ?? () from /usr/lib/libQtGui.so.4
#32 0xb68476a8 in QApplication::x11ProcessEvent () from /usr/lib/libQtGui.so.4
#33 0xb6873c6a in ?? () from /usr/lib/libQtGui.so.4
#34 0xb4e30b88 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#35 0xb4e340eb in ?? () from /usr/lib/libglib-2.0.so.0
#36 0xb4e34268 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#37 0xb6550438 in QEventDispatcherGlib::processEvents () from /usr/lib/libQtCore.so.4
#38 0xb6873365 in ?? () from /usr/lib/libQtGui.so.4
#39 0xb652306a in QEventLoop::processEvents () from /usr/lib/libQtCore.so.4
#40 0xb65234aa in QEventLoop::exec () from /usr/lib/libQtCore.so.4
#41 0xb6525959 in QCoreApplication::exec () from /usr/lib/libQtCore.so.4
#42 0xb67d1d17 in QApplication::exec () from /usr/lib/libQtGui.so.4
#43 0xb7e9eb56 in kdemain () from /usr/lib/libkdeinit4_plasma.so
#44 0x08048712 in _start ()

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