a more detailed backtrace is required; please consult this page for how to do that:

http://techbase.kde.org/Development/Tutorials/Debugging/How_to_create_useful_crash_reports

thanks in advance ...

Sorry guys, I didn't know that I had to install the debug packages. I installed them and I'm ready for the next plasma crash :)
You can probably close this bug if you think it's useless.

try and duplicate the crash, and if you can then paste the results here. if you can't replicate the crash then we'll probably close this report for now as "NEEDSINFO"

Ok, I did it again. Here is the new backtrace. The crash happened exactly like before. 

Application: Plasma Workspace (plasma-desktop), signal: Aborted
[Current thread is 1 (Thread 0x7f729c884740 (LWP 3720))]

Thread 2 (Thread 0x7f727d704950 (LWP 4009)):
#0  0x00007f7295740f69 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
#1  0x00007f72993ef2b9 in QWaitCondition::wait () from /usr/lib64/libQtCore.so.4
#2  0x00007f7296205adc in ?? () from /usr/lib64/libQtNetwork.so.4
#3  0x00007f72993ee2d2 in ?? () from /usr/lib64/libQtCore.so.4
#4  0x00007f729573d263 in start_thread () from /lib64/libpthread.so.0
#5  0x00007f729c28978d in clone () from /lib64/libc.so.6

Thread 1 (Thread 0x7f729c884740 (LWP 3720)):
[KCrash Handler]
#5  0x00007f729c1dda15 in raise () from /lib64/libc.so.6
#6  0x00007f729c1df243 in abort () from /lib64/libc.so.6
#7  0x00007f72993e62c5 in qt_message_output () from /usr/lib64/libQtCore.so.4
#8  0x00007f72993e640b in qFatal () from /usr/lib64/libQtCore.so.4
#9  0x00007f727f486294 in KSharedPtr<TaskManager::Task>::operator-> (this=0x7fffa49b0f60) at /usr/include/ksharedptr.h:126
#10 0x00007f727f490182 in AbstractTaskItem::timerEvent (this=0x1c9ce90, event=<value optimized out>) at /usr/src/debug/kdebase-workspace-4.2.85/plasma/applets/tasks/abstracttaskitem.cpp:400
#11 0x00007f72994e72d3 in QObject::event () from /usr/lib64/libQtCore.so.4
#12 0x00007f729a1e5d8b in QGraphicsWidget::event () from /usr/lib64/libQtGui.so.4
#13 0x00007f7299bcc0ed in QApplicationPrivate::notify_helper () from /usr/lib64/libQtGui.so.4
#14 0x00007f7299bd435a in QApplication::notify () from /usr/lib64/libQtGui.so.4
#15 0x00007f729ac76e3e in KApplication::notify (this=0x123d680, receiver=0x1c9ce90, event=0x7fffa49b3730) at /usr/src/debug/kdelibs-4.2.85/kdeui/kernel/kapplication.cpp:307
#16 0x00007f72994d753c in QCoreApplication::notifyInternal () from /usr/lib64/libQtCore.so.4
#17 0x00007f7299504596 in ?? () from /usr/lib64/libQtCore.so.4
#18 0x00007f7299500c8d in ?? () from /usr/lib64/libQtCore.so.4
#19 0x00007f7293d2d611 in g_main_context_dispatch () from /usr/lib64/libglib-2.0.so.0
#20 0x00007f7293d30cc0 in ?? () from /usr/lib64/libglib-2.0.so.0
#21 0x00007f7293d30e5c in g_main_context_iteration () from /usr/lib64/libglib-2.0.so.0
#22 0x00007f7299500bef in QEventDispatcherGlib::processEvents () from /usr/lib64/libQtCore.so.4
#23 0x00007f7299c6396f in ?? () from /usr/lib64/libQtGui.so.4
#24 0x00007f72994d5de2 in QEventLoop::processEvents () from /usr/lib64/libQtCore.so.4
#25 0x00007f72994d61ad in QEventLoop::exec () from /usr/lib64/libQtCore.so.4
#26 0x00007f72994d8474 in QCoreApplication::exec () from /usr/lib64/libQtCore.so.4
#27 0x00007f729c5496fb in kdemain (argc=1, argv=0x7fffa49b3cf8) at /usr/src/debug/kdebase-workspace-4.2.85/plasma/shells/desktop/main.cpp:50
#28 0x00007f729c1ca446 in __libc_start_main () from /lib64/libc.so.6
#29 0x0000000000400609 in _start () at ../sysdeps/x86_64/elf/start.S:113

Sorry, I just realized that there are still lots of question marks there. I just installed the qt-debug packages. I'll try to make it crash one more time.

OK, here it is. I hope it is complete this time.

Application: Plasma Workspace (plasma-desktop), signal: Aborted
[Current thread is 1 (Thread 0x7fec2ad70740 (LWP 5451))]

Thread 2 (Thread 0x7fec0bc11950 (LWP 5452)):
#0  0x00007fec23c2cf69 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
#1  0x00007fec278db2b9 in QWaitCondition::wait (this=0x210d580, mutex=0x210d578, time=18446744073709551615) at thread/qwaitcondition_unix.cpp:87
#2  0x00007fec246f1adc in QHostInfoAgent::run (this=0x210d560) at kernel/qhostinfo.cpp:260
#3  0x00007fec278da2d2 in QThreadPrivate::start (arg=0x210d560) at thread/qthread_unix.cpp:189
#4  0x00007fec23c29263 in start_thread () from /lib64/libpthread.so.0
#5  0x00007fec2a77578d in clone () from /lib64/libc.so.6

Thread 1 (Thread 0x7fec2ad70740 (LWP 5451)):
[KCrash Handler]
#5  0x00007fec2a6c9a15 in raise () from /lib64/libc.so.6
#6  0x00007fec2a6cb243 in abort () from /lib64/libc.so.6
#7  0x00007fec278d22c5 in qt_message_output (msgType=QtFatalMsg, buf=<value optimized out>) at global/qglobal.cpp:2017
#8  0x00007fec278d240b in qFatal (msg=<value optimized out>) at global/qglobal.cpp:2216
#9  0x00007fec0d993294 in KSharedPtr<TaskManager::Task>::operator-> (this=0x7fff32e9d620) at /usr/include/ksharedptr.h:126
#10 0x00007fec0d99d182 in AbstractTaskItem::timerEvent (this=0x2568ae0, event=<value optimized out>) at /usr/src/debug/kdebase-workspace-4.2.85/plasma/applets/tasks/abstracttaskitem.cpp:400
#11 0x00007fec279d32d3 in QObject::event (this=0x2568ae0, e=0x154b) at kernel/qobject.cpp:1073
#12 0x00007fec286d1d8b in QGraphicsWidget::event (this=0x2568ae0, event=0x7fff32e9fdf0) at graphicsview/qgraphicswidget.cpp:1340
#13 0x00007fec280b80ed in QApplicationPrivate::notify_helper (this=0x1a09b40, receiver=0x2568ae0, e=0x7fff32e9fdf0) at kernel/qapplication.cpp:4057
#14 0x00007fec280c035a in QApplication::notify (this=0x19f1680, receiver=0x2568ae0, e=0x7fff32e9fdf0) at kernel/qapplication.cpp:4022
#15 0x00007fec29162e3e in KApplication::notify (this=0x19f1680, receiver=0x2568ae0, event=0x7fff32e9fdf0) at /usr/src/debug/kdelibs-4.2.85/kdeui/kernel/kapplication.cpp:307
#16 0x00007fec279c353c in QCoreApplication::notifyInternal (this=0x19f1680, receiver=0x2568ae0, event=0x7fff32e9fdf0) at kernel/qcoreapplication.cpp:610
#17 0x00007fec279f0596 in QTimerInfoList::activateTimers (this=0x1a0d370) at ../../src/corelib/kernel/qcoreapplication.h:213
#18 0x00007fec279ecc8d in timerSourceDispatch (source=<value optimized out>) at kernel/qeventdispatcher_glib.cpp:164
#19 0x00007fec22219611 in g_main_context_dispatch () from /usr/lib64/libglib-2.0.so.0
#20 0x00007fec2221ccc0 in ?? () from /usr/lib64/libglib-2.0.so.0
#21 0x00007fec2221ce5c in g_main_context_iteration () from /usr/lib64/libglib-2.0.so.0
#22 0x00007fec279ecbef in QEventDispatcherGlib::processEvents (this=0x19d7df0, flags=<value optimized out>) at kernel/qeventdispatcher_glib.cpp:324
#23 0x00007fec2814f96f in QGuiEventDispatcherGlib::processEvents (this=0x154b, flags=<value optimized out>) at kernel/qguieventdispatcher_glib.cpp:202
#24 0x00007fec279c1de2 in QEventLoop::processEvents (this=<value optimized out>, flags={i = 854196320}) at kernel/qeventloop.cpp:149
#25 0x00007fec279c21ad in QEventLoop::exec (this=0x7fff32ea00a0, flags={i = 854196400}) at kernel/qeventloop.cpp:200
#26 0x00007fec279c4474 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:888
#27 0x00007fec2aa356fb in kdemain (argc=1, argv=0x7fff32ea03b8) at /usr/src/debug/kdebase-workspace-4.2.85/plasma/shells/desktop/main.cpp:50
#28 0x00007fec2a6b6446 in __libc_start_main () from /lib64/libc.so.6
#29 0x0000000000400609 in _start () at ../sysdeps/x86_64/elf/start.S:113

I see a question mark at #20 but I don't have a debug package for libglib. What should I install to complete the backtrace?

I installed glibc-debug. Still no dice.

*** This bug has been marked as a duplicate of bug 191412 ***