Version:            (using Devel)
Compiler:          gcc version 4.4.0 
OS:                Linux
Installed from:    Compiled sources

Here is the exact way to reproduce this bug.

1. Add a widget the the desktop (say the calculator widget)
2. Drag it into the panel and click it.
3. Go into panel editing mode and drag the widget onto the desktop.
4. Now close the widget and then click the KMenu.

It should crash plasma every time with virtually any widget.

Backtrace

Application: Plasma Workspace (plasma-desktop), signal: Segmentation fault
[Current thread is 0 (LWP 689)]

Thread 2 (Thread 0x7f65445d0950 (LWP 690)):
#0  0x00007f655f5ddbe9 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/libpthread.so.0
#1  0x00007f655f84dc59 in QWaitCondition::wait () from /usr/lib/libQtCore.so.4
#2  0x00007f656300e2fc in ?? () from /usr/lib/libQtNetwork.so.4
#3  0x00007f655f84cc62 in ?? () from /usr/lib/libQtCore.so.4
#4  0x00007f655f5d93b4 in start_thread () from /lib/libpthread.so.0
#5  0x00007f655eba789d in clone () from /lib/libc.so.6

Thread 1 (Thread 0x7f65646547a0 (LWP 689)):
[KCrash Handler]
#5  0x0000000002e32890 in ?? ()
#6  0x00007f6563d588f3 in Plasma::ContainmentPrivate::focusApplet (this=0x23036d0, applet=0x228f0b0) at /home/sean/Compiled/trunk/kdelibs/plasma/containment.cpp:1549
#7  0x00007f6563d4521e in Plasma::Applet::focusInEvent (this=0x228f0b0, event=0x7fff6c793c60) at /home/sean/Compiled/trunk/kdelibs/plasma/applet.cpp:1493
#8  0x00007f6560609bfd in QGraphicsItem::sceneEvent () from /usr/lib/libQtGui.so.4
#9  0x00007f656062f988 in QGraphicsScene::setFocusItem () from /usr/lib/libQtGui.so.4
#10 0x00007f656063bdc9 in ?? () from /usr/lib/libQtGui.so.4
#11 0x00007f656063c970 in QGraphicsScene::event () from /usr/lib/libQtGui.so.4
#12 0x00007f656003e40d in QApplicationPrivate::notify_helper () from /usr/lib/libQtGui.so.4
#13 0x00007f656004668a in QApplication::notify () from /usr/lib/libQtGui.so.4
#14 0x00007f6562928cee in KApplication::notify (this=0x20d83e0, receiver=0x2217630, event=0x7fff6c794430) at /home/sean/Compiled/trunk/kdelibs/kdeui/kernel/kapplication.cpp:307
#15 0x00007f655f93539c in QCoreApplication::notifyInternal () from /usr/lib/libQtCore.so.4
#16 0x00007f656064895d in QGraphicsView::mousePressEvent () from /usr/lib/libQtGui.so.4
#17 0x00007f656008f836 in QWidget::event () from /usr/lib/libQtGui.so.4
#18 0x00007f656042a58b in QFrame::event () from /usr/lib/libQtGui.so.4
#19 0x00007f656064d0bb in QGraphicsView::viewportEvent () from /usr/lib/libQtGui.so.4
#20 0x00007f655f9346a8 in QCoreApplicationPrivate::sendThroughObjectEventFilters () from /usr/lib/libQtCore.so.4
#21 0x00007f656003e3dc in QApplicationPrivate::notify_helper () from /usr/lib/libQtGui.so.4
#22 0x00007f6560046dea in QApplication::notify () from /usr/lib/libQtGui.so.4
#23 0x00007f6562928cee in KApplication::notify (this=0x20d83e0, receiver=0x244cc60, event=0x7fff6c794e40) at /home/sean/Compiled/trunk/kdelibs/kdeui/kernel/kapplication.cpp:307
#24 0x00007f655f93539c in QCoreApplication::notifyInternal () from /usr/lib/libQtCore.so.4
#25 0x00007f6560046038 in QApplicationPrivate::sendMouseEvent () from /usr/lib/libQtGui.so.4
#26 0x00007f65600aff19 in ?? () from /usr/lib/libQtGui.so.4
#27 0x00007f65600aec5d in QApplication::x11ProcessEvent () from /usr/lib/libQtGui.so.4
#28 0x00007f65600d6354 in ?? () from /usr/lib/libQtGui.so.4
#29 0x00007f655b1ec01a in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#30 0x00007f655b1ef6e0 in g_main_context_iterate () from /usr/lib/libglib-2.0.so.0
#31 0x00007f655b1ef87c in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#32 0x00007f655f95ea0f in QEventDispatcherGlib::processEvents () from /usr/lib/libQtCore.so.4
#33 0x00007f65600d5aff in ?? () from /usr/lib/libQtGui.so.4
#34 0x00007f655f933c42 in QEventLoop::processEvents () from /usr/lib/libQtCore.so.4
#35 0x00007f655f93400d in QEventLoop::exec () from /usr/lib/libQtCore.so.4
#36 0x00007f655f9362d4 in QCoreApplication::exec () from /usr/lib/libQtCore.so.4
#37 0x00007f656432bd00 in kdemain (argc=<value optimized out>, argv=<value optimized out>) at /home/sean/Compiled/trunk/kdebase/workspace/plasma/shells/desktop/main.cpp:50
#38 0x00007f655eafa55d in __libc_start_main () from /lib/libc.so.6
#39 0x00000000004007d9 in _start ()