As you can reproduce the crash at will, may you read http://techbase.kde.org/Development/Tutorials/Debugging/How_to_create_useful_crash_reports and post a complete backtrace here? 
If you don't get the crash handler dialog, you may need to use GDB (I can teach you some of the basics if you need it)
Thanks

BTW, this could be related to bug 199787.
Marking as NEEDSINFO

Here is the backtrace. 
It is not complete because I haven't found the dbg symbols for network-manager-plasmoid that it is where it crahes. But anyway here it goes.
................................................
This backtrace appears to be of no use.
This is probably because your packages are built in a way which prevents creation of proper backtraces, or the stack frame was seriously corrupted in the crash.

[Thread debugging using libthread_db enabled]
[New Thread 0xb3c55730 (LWP 10556)]
[New Thread 0x9e0d0b90 (LWP 10574)]
[New Thread 0xa3dffb90 (LWP 10573)]
[New Thread 0xa4713b90 (LWP 10568)]
[New Thread 0xa0718b90 (LWP 10567)]
[New Thread 0xa4f1ab90 (LWP 10561)]
[New Thread 0xa57a4b90 (LWP 10560)]
[New Thread 0xa6e5eb90 (LWP 10557)]
0xb7f37430 in __kernel_vsyscall ()
[Current thread is 0 (LWP 10556)]

Thread 8 (Thread 0xa6e5eb90 (LWP 10557)):
#0  0xb7f37430 in __kernel_vsyscall ()
#1  0xb506f0e5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb627e2ed in pthread_cond_wait () from /lib/tls/i686/cmov/libc.so.6
#3  0xb646a9b2 in QWaitCondition::wait (this=0x90dda80, mutex=0x90dda7c, time=4294967295) at thread/qwaitcondition_unix.cpp:87
#4  0xb78eb152 in QHostInfoAgent::run (this=0x90dda70) at kernel/qhostinfo.cpp:260
#5  0xb646996e in QThreadPrivate::start (arg=0x90dda70) at thread/qthread_unix.cpp:189
#6  0xb506b4ff in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#7  0xb626f49e in clone () from /lib/tls/i686/cmov/libc.so.6

Thread 7 (Thread 0xa57a4b90 (LWP 10560)):
#0  0xb7f37430 in __kernel_vsyscall ()
#1  0xb506f412 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb627e344 in pthread_cond_timedwait () from /lib/tls/i686/cmov/libc.so.6
#3  0xa63a0ae3 in ?? () from /usr/lib/libxine.so.1

Thread 6 (Thread 0xa4f1ab90 (LWP 10561)):
#0  0xb4e6d22b in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#1  0xb6589457 in QEventDispatcherGlib::processEvents (this=0x92e3800, flags={i = -1527668168}) at kernel/qeventdispatcher_glib.cpp:325
#2  0xb655c06a in QEventLoop::processEvents (this=0xa4f1a2b0, flags={i = -1527668104}) at kernel/qeventloop.cpp:149
#3  0xb655c4aa in QEventLoop::exec (this=0xa4f1a2b0, flags={i = -1527668040}) at kernel/qeventloop.cpp:200
#4  0xb6466639 in QThread::exec (this=0x92e2128) at thread/qthread.cpp:481
#5  0xa63ee20a in ?? () from /usr/lib/kde4/plugins/phonon_backend/phonon_xine.so
#6  0xb646996e in QThreadPrivate::start (arg=0x92e2128) at thread/qthread_unix.cpp:189
#7  0xb506b4ff in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#8  0xb626f49e in clone () from /lib/tls/i686/cmov/libc.so.6

Thread 5 (Thread 0xa0718b90 (LWP 10567)):
#0  0xb7f37430 in __kernel_vsyscall ()
#1  0xb6264ae7 in poll () from /lib/tls/i686/cmov/libc.so.6
#2  0xa4f97b19 in ?? () from /usr/lib/xine/plugins/1.26/xineplug_ao_out_alsa.so
#3  0xa6502514 in ?? ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

Thread 4 (Thread 0xa4713b90 (LWP 10568)):
#0  0xb7f37430 in __kernel_vsyscall ()
#1  0xb506f0e5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb627e2ed in pthread_cond_wait () from /lib/tls/i686/cmov/libc.so.6
#3  0xa63b1d8e in ?? () from /usr/lib/libxine.so.1
#4  0x00000001 in ?? ()

Thread 3 (Thread 0xa3dffb90 (LWP 10573)):
#0  0xb7f37430 in __kernel_vsyscall ()
#1  0xb506f0e5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb627e2ed in pthread_cond_wait () from /lib/tls/i686/cmov/libc.so.6
#3  0xb646a9b2 in QWaitCondition::wait (this=0x8c99d40, mutex=0x8c99d3c, time=4294967295) at thread/qwaitcondition_unix.cpp:87
#4  0xa8564b9a in RenderThread::run (this=0x8c99d34) at /build/buildd/kdebase-workspace-4.2.2/plasma/wallpapers/image/renderthread.cpp:91
#5  0xb646996e in QThreadPrivate::start (arg=0x8c99d34) at thread/qthread_unix.cpp:189
#6  0xb506b4ff in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#7  0xb626f49e in clone () from /lib/tls/i686/cmov/libc.so.6

Thread 2 (Thread 0x9e0d0b90 (LWP 10574)):
#0  0xb7f37430 in __kernel_vsyscall ()
#1  0xb506f0e5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb627e2ed in pthread_cond_wait () from /lib/tls/i686/cmov/libc.so.6
#3  0xb646a9b2 in QWaitCondition::wait (this=0x8cd4d68, mutex=0x8cd4d64, time=4294967295) at thread/qwaitcondition_unix.cpp:87
#4  0xa8564b9a in RenderThread::run (this=0x8cd4d5c) at /build/buildd/kdebase-workspace-4.2.2/plasma/wallpapers/image/renderthread.cpp:91
#5  0xb646996e in QThreadPrivate::start (arg=0x8cd4d5c) at thread/qthread_unix.cpp:189
#6  0xb506b4ff in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#7  0xb626f49e in clone () from /lib/tls/i686/cmov/libc.so.6

Thread 1 (Thread 0xb3c55730 (LWP 10556)):
#0  0xb7f37430 in __kernel_vsyscall ()
#1  0xb622a7a6 in nanosleep () from /lib/tls/i686/cmov/libc.so.6
#2  0xb622a5be in sleep () from /lib/tls/i686/cmov/libc.so.6
#3  0xb76d28b2 in ?? () from /usr/lib/libkdeui.so.5
#4  0xb76d3274 in KCrash::defaultCrashHandler () from /usr/lib/libkdeui.so.5
#5  <signal handler called>
#6  0xa86091ad in ?? () from /usr/lib/kde4/plasma_applet_networkmanagement.so
#7  0xa861b7dd in ?? () from /usr/lib/kde4/plasma_applet_networkmanagement.so
#8  0xa8606bfb in ?? () from /usr/lib/kde4/plasma_applet_networkmanagement.so
#9  0xb6573ca8 in QMetaObject::activate (sender=0x9171aa0, from_signal_index=5, to_signal_index=5, argv=0x0) at kernel/qobject.cpp:3069
#10 0xb6574932 in QMetaObject::activate (sender=0x9171aa0, m=0xa8638fe0, local_signal_index=0, argv=0x0) at kernel/qobject.cpp:3143
#11 0xa86059d7 in ?? () from /usr/lib/kde4/plasma_applet_networkmanagement.so
#12 0xa860b2e2 in ?? () from /usr/lib/kde4/plasma_applet_networkmanagement.so
#13 0xa8606b03 in ?? () from /usr/lib/kde4/plasma_applet_networkmanagement.so
#14 0xa8606bba in ?? () from /usr/lib/kde4/plasma_applet_networkmanagement.so
#15 0xb6573ca8 in QMetaObject::activate (sender=0x8c95798, from_signal_index=8, to_signal_index=8, argv=0xbfe524c8) at kernel/qobject.cpp:3069
#16 0xb6574932 in QMetaObject::activate (sender=0x8c95798, m=0xa85d9e44, local_signal_index=1, argv=0xbfe524c8) at kernel/qobject.cpp:3143
#17 0xa85d2b09 in NetworkManagerSettings::connectionRemoved () from /usr/lib/libknmdbus.so.4
#18 0xa85d4106 in NetworkManagerSettings::onConnectionRemoved () from /usr/lib/libknmdbus.so.4
#19 0xa85d488b in NetworkManagerSettings::qt_metacall () from /usr/lib/libknmdbus.so.4
#20 0xb6573ca8 in QMetaObject::activate (sender=0x8c955a8, from_signal_index=5, to_signal_index=5, argv=0x0) at kernel/qobject.cpp:3069
#21 0xb6574932 in QMetaObject::activate (sender=0x8c955a8, m=0xa85d9d24, local_signal_index=0, argv=0x0) at kernel/qobject.cpp:3143
#22 0xa85d10c7 in OrgFreedesktopNetworkManagerSettingsConnectionInterface::Removed () from /usr/lib/libknmdbus.so.4
#23 0xa85d16c3 in OrgFreedesktopNetworkManagerSettingsConnectionInterface::qt_metacall () from /usr/lib/libknmdbus.so.4
#24 0xa85d0192 in RemoteConnection::qt_metacall () from /usr/lib/libknmdbus.so.4
#25 0xb6676d7a in QDBusConnectionPrivate::deliverCall (this=0x8b3e6d8, object=0x8c955a8, msg=@0x9cfba4c, metaTypes=@0x9cfba50, slotIdx=5) at qdbusintegrator.cpp:891
#26 0xb667f187 in QDBusCallDeliveryEvent::placeMetaCall (this=0x9cfba20, object=0x8c955a8) at qdbusintegrator_p.h:101
#27 0xb656e3a0 in QObject::event (this=0x8c955a8, e=0x9cfba20) at kernel/qobject.cpp:1118
#28 0xb680ae9c in QApplicationPrivate::notify_helper (this=0x89e67b8, receiver=0x8c955a8, e=0x9cfba20) at kernel/qapplication.cpp:4084
#29 0xb681319e in QApplication::notify (this=0x89c7728, receiver=0x8c955a8, e=0x9cfba20) at kernel/qapplication.cpp:3631
#30 0xb766294d in KApplication::notify () from /usr/lib/libkdeui.so.5
#31 0xb655da3b in QCoreApplication::notifyInternal (this=0x89c7728, receiver=0x89c7728, event=0x9cfba20) at kernel/qcoreapplication.cpp:602
#32 0xb655e695 in QCoreApplicationPrivate::sendPostedEvents (receiver=0x0, event_type=0, data=0x89a54b8) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:213
#33 0xb655e88d in QCoreApplication::sendPostedEvents (receiver=0x0, event_type=0) at kernel/qcoreapplication.cpp:1132
#34 0xb65897ef in postEventSourceDispatch (s=0x89e9310) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:218
#35 0xb4e69b88 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#36 0xb4e6d0eb in ?? () from /usr/lib/libglib-2.0.so.0
#37 0xb4e6d268 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#38 0xb6589438 in QEventDispatcherGlib::processEvents (this=0x89a82e0, flags={i = -1075499448}) at kernel/qeventdispatcher_glib.cpp:323
#39 0xb68ac365 in QGuiEventDispatcherGlib::processEvents (this=0x89a82e0, flags={i = -1075499400}) at kernel/qguieventdispatcher_glib.cpp:202
#40 0xb655c06a in QEventLoop::processEvents (this=0xbfe52ef0, flags={i = -1075499336}) at kernel/qeventloop.cpp:149
#41 0xb655c4aa in QEventLoop::exec (this=0xbfe52ef0, flags={i = -1075499272}) at kernel/qeventloop.cpp:200
#42 0xb655e959 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:880
#43 0xb680ad17 in QApplication::exec () at kernel/qapplication.cpp:3553
#44 0xb7ed8b56 in kdemain (argc=1, argv=0xbfe530a4) at /build/buildd/kdebase-workspace-4.2.2/plasma/shells/desktop/main.cpp:54
#45 0x08048712 in main (argc=-1469868376, argv=0x9172570) at /build/buildd/kdebase-workspace-4.2.2/obj-i486-linux-gnu/plasma/shells/desktop/plasma_qgv_dummy.cpp:3
#0  0xb7f37430 in __kernel_vsyscall ()

This is likely to be bug 192790. Thanks

*** This bug has been marked as a duplicate of bug 192790 ***