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

At about the same moment, FireFox popped up a notification to say it had finished downloading a file (to a folder that isn't used by any folderview or similar) and in Bilbo Blogger, which I was using, I pushed the "reload" button under the Post Categories tab. About 1/2 a second later Plasma crashed and brought up the following backtrace in the KDE Crash Handler:

Application: Plasma Workspace (plasma), signal SIGSEGV
0x00007f66c7887d21 in nanosleep () from /lib/libc.so.6
[Current thread is 0 (LWP 3720)]

Thread 3 (Thread 0x7f66ae370950 (LWP 3721)):
#0  0x00007f66c4f3f2e9 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/libpthread.so.0
#1  0x00007f66c8369939 in QWaitCondition::wait () from /usr/lib/libQtCore.so.4
#2  0x00007f66cbb254cc in ?? () from /usr/lib/libQtNetwork.so.4
#3  0x00007f66c8368952 in ?? () from /usr/lib/libQtCore.so.4
#4  0x00007f66c4f3b3ba in start_thread () from /lib/libpthread.so.0
#5  0x00007f66c78c5fcd in clone () from /lib/libc.so.6
#6  0x0000000000000000 in ?? ()

Thread 2 (Thread 0x7f66ad969950 (LWP 3722)):
#0  0x00007f66c4f3f2e9 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/libpthread.so.0
#1  0x00007f66c8369939 in QWaitCondition::wait () from /usr/lib/libQtCore.so.4
#2  0x00007f66af074d4e in ?? () from /usr/lib/kde4/plasma_wallpaper_image.so
#3  0x00007f66c8368952 in ?? () from /usr/lib/libQtCore.so.4
#4  0x00007f66c4f3b3ba in start_thread () from /lib/libpthread.so.0
#5  0x00007f66c78c5fcd in clone () from /lib/libc.so.6
#6  0x0000000000000000 in ?? ()

Thread 1 (Thread 0x7f66cce48760 (LWP 3720)):
[KCrash Handler]
#5  0x00007f66c8468aa5 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#6  0x00007f66b0a6874f in TaskManager::AbstractGroupingStrategy::groupRemoved () from /usr/lib/libtaskmanager.so.4
#7  0x00007f66b0a69d2e in TaskManager::AbstractGroupingStrategy::closeGroup () from /usr/lib/libtaskmanager.so.4
#8  0x00007f66b0a70328 in ?? () from /usr/lib/libtaskmanager.so.4
#9  0x00007f66b0a70f0d in ?? () from /usr/lib/libtaskmanager.so.4
#10 0x00007f66c84671f2 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#11 0x00007f66b0a807f2 in TaskManager::TaskGroup::itemRemoved () from /usr/lib/libtaskmanager.so.4
#12 0x00007f66b0a6c008 in TaskManager::GroupManager::remove () from /usr/lib/libtaskmanager.so.4
#13 0x00007f66b0a6dbcb in TaskManager::GroupManager::qt_metacall () from /usr/lib/libtaskmanager.so.4
#14 0x00007f66c84671f2 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#15 0x00007f66b0a83c15 in TaskManager::TaskManager::taskRemoved () from /usr/lib/libtaskmanager.so.4
#16 0x00007f66b0a850e9 in TaskManager::TaskManager::windowRemoved () from /usr/lib/libtaskmanager.so.4
#17 0x00007f66b0a86ddf in TaskManager::TaskManager::qt_metacall () from /usr/lib/libtaskmanager.so.4
#18 0x00007f66c84671f2 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#19 0x00007f66cb37dd92 in KWindowSystem::windowRemoved () from /usr/lib/libkdeui.so.5
#20 0x00007f66cb3802db in ?? () from /usr/lib/libkdeui.so.5
#21 0x00007f66cb38f141 in NETRootInfo::update () from /usr/lib/libkdeui.so.5
#22 0x00007f66cb38f4cb in NETRootInfo::event () from /usr/lib/libkdeui.so.5
#23 0x00007f66cb3805ab in ?? () from /usr/lib/libkdeui.so.5
#24 0x00007f66cb252683 in KApplication::x11EventFilter () from /usr/lib/libkdeui.so.5
#25 0x00007f66ccbc33b4 in ?? () from /usr/lib/libkdeinit4_plasma.so
#26 0x00007f66c8bf2bcf in ?? () from /usr/lib/libQtGui.so.4
#27 0x00007f66c8c0605f in QApplication::x11ProcessEvent () from /usr/lib/libQtGui.so.4
#28 0x00007f66c8c2f514 in ?? () from /usr/lib/libQtGui.so.4
#29 0x00007f66c330b20a in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#30 0x00007f66c330e8e0 in ?? () from /usr/lib/libglib-2.0.so.0
#31 0x00007f66c330ea7c in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#32 0x00007f66c847ae6f in QEventDispatcherGlib::processEvents () from /usr/lib/libQtCore.so.4
#33 0x00007f66c8c2ec9f in ?? () from /usr/lib/libQtGui.so.4
#34 0x00007f66c8450002 in QEventLoop::processEvents () from /usr/lib/libQtCore.so.4
#35 0x00007f66c84503cd in QEventLoop::exec () from /usr/lib/libQtCore.so.4
#36 0x00007f66c8452694 in QCoreApplication::exec () from /usr/lib/libQtCore.so.4
#37 0x00007f66ccbb29bb in kdemain () from /usr/lib/libkdeinit4_plasma.so
#38 0x00007f66c77fe5a6 in __libc_start_main () from /lib/libc.so.6
#39 0x00000000004007c9 in _start ()