Version:           4.1 beta1 (using Devel)
Installed from:    Compiled sources
OS:                Linux

I got this backtrace when I was about to spread the plasma button (hover):

Aplicación: Área de trabajo de Plasma (plasma), señal SIGSEGV
[Thread debugging using libthread_db enabled]
[New Thread 0x7fa648dc8780 (LWP 690)]
[New Thread 0x41c52950 (LWP 691)]
[KCrash handler]
#5  0x0000000000000090 in ?? ()
#6  0x00007fa64768ff28 in QObject::disconnect (sender=0x231f060, 
    signal=0x228f269 "deviceAdded(QString)", receiver=0x22cbac0, 
    method=0x2235989 "deviceAdded(QString)") at kernel/qobject.cpp:2571
#7  0x00007fa635e0b398 in ~SolidDeviceEngine (this=0x22cbac0)
    at /tmp/buildd/kdebase-workspace-4.0.80/plasma/dataengines/soliddevice/soliddeviceengine.cpp:67
#8  0x00007fa64848de8b in ~DataEngineManager (this=0x22876f0)
    at /tmp/buildd/kdebase-workspace-4.0.80/libs/plasma/dataenginemanager.cpp:55
#9  0x00007fa64848e0f7 in destroy ()
    at /tmp/buildd/kdebase-workspace-4.0.80/libs/plasma/dataenginemanager.cpp:75
#10 0x00007fa6487a4bd0 in exit () from /lib/libc.so.6
#11 0x00007fa647591d0a in qt_message_output (msgType=QtFatalMsg, 
    buf=<value optimized out>) at global/qglobal.cpp:2060
#12 0x00007fa647591e57 in qFatal (msg=<value optimized out>)
    at global/qglobal.cpp:2260
#13 0x00007fa64847cb07 in Plasma::Containment::sceneEventFilter (
    this=0x210db80, watched=0x26bb880, event=0x7fff50ef9b10)
    at /tmp/buildd/kdebase-workspace-4.0.80/libs/plasma/containment.cpp:737
#14 0x00007fa646ed4ed1 in QGraphicsScenePrivate::filterEvent (this=0x20cf740, 
    item=0x26bb880, event=0x7fff50ef9b10)
    at graphicsview/qgraphicsscene.cpp:1026
#15 0x00007fa646ed4f59 in QGraphicsScenePrivate::sendEvent (this=0x231f060, 
    item=0x22cbac0, event=0x2235988) at graphicsview/qgraphicsscene.cpp:1044
#16 0x00007fa646ed51bd in QGraphicsScenePrivate::sendHoverEvent (
    this=0x20cf740, type=<value optimized out>, item=0x26bb880, 
    hoverEvent=0x7fff50ef9ca0) at graphicsview/qgraphicsscene.cpp:1093
#17 0x00007fa646ee125c in QGraphicsScenePrivate::dispatchHoverEvent (
    this=0x20cf740, hoverEvent=0x7fff50ef9ca0)
    at graphicsview/qgraphicsscene.cpp:3421
#18 0x00007fa646ee15a9 in QGraphicsScene::mouseMoveEvent (
    this=<value optimized out>, mouseEvent=0x7fff50efa180)
    at graphicsview/qgraphicsscene.cpp:3566
#19 0x00007fa646ee179f in QGraphicsScene::event (this=0x20cf350, 
    event=0x7fff50efa180) at graphicsview/qgraphicsscene.cpp:2984
#20 0x00007fa6469b24df in QApplicationPrivate::notify_helper (this=0x1fea260, 
    receiver=0x20cf350, e=0x7fff50efa180) at kernel/qapplication.cpp:3772
#21 0x00007fa6469b70b5 in QApplication::notify (this=0x1fe0960, 
    receiver=0x20cf350, e=0x7fff50efa180) at kernel/qapplication.cpp:3739
#22 0x00007fa647ff2d2b in KApplication::notify (this=0x1fe0960, 
    receiver=0x20cf350, event=0x7fff50efa180)
    at /tmp/buildd/kde4libs-4.0.80/kdeui/kernel/kapplication.cpp:311
#23 0x00007fa64767abd9 in QCoreApplication::notifyInternal (this=0x1fe0960, 
    receiver=0x20cf350, event=0x7fff50efa180)
    at kernel/qcoreapplication.cpp:587
#24 0x00007fa646ef1dab in QGraphicsView::mouseMoveEvent (this=0x2298960, 
    event=0x7fff50efabc0)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:215
#25 0x00007fa646a00442 in QWidget::event (this=0x2298960, 
    event=0x7fff50efabc0) at kernel/qwidget.cpp:6912
#26 0x00007fa646cfe6d6 in QFrame::event (this=0x2298960, e=0x7fff50efabc0)
    at widgets/qframe.cpp:657
#27 0x00007fa646d82d49 in QAbstractScrollArea::viewportEvent (this=0x231f060, 
    e=0x22cbac0) at widgets/qabstractscrollarea.cpp:941
#28 0x00007fa646eef2b1 in QGraphicsView::viewportEvent (this=0x2298960, 
    event=0x7fff50efabc0) at graphicsview/qgraphicsview.cpp:2267
#29 0x00007fa646d83ee8 in QAbstractScrollAreaFilter::eventFilter (
    this=<value optimized out>, o=<value optimized out>, e=0x2235988)
    at widgets/qabstractscrollarea_p.h:102
#30 0x00007fa64767aede in QCoreApplicationPrivate::sendThroughObjectEventFilters (this=<value optimized out>, receiver=0x2299050, event=0x7fff50efabc0)
    at kernel/qcoreapplication.cpp:694
#31 0x00007fa6469b24b0 in QApplicationPrivate::notify_helper (this=0x1fea260, 
    receiver=0x2299050, e=0x7fff50efabc0) at kernel/qapplication.cpp:3768
#32 0x00007fa6469b72b9 in QApplication::notify (this=0x1fe0960, 
    receiver=0x2299050, e=0x7fff50efabc0) at kernel/qapplication.cpp:3501
#33 0x00007fa647ff2d2b in KApplication::notify (this=0x1fe0960, 
    receiver=0x2299050, event=0x7fff50efabc0)
    at /tmp/buildd/kde4libs-4.0.80/kdeui/kernel/kapplication.cpp:311
#34 0x00007fa64767abd9 in QCoreApplication::notifyInternal (this=0x1fe0960, 
    receiver=0x2299050, event=0x7fff50efabc0)
    at kernel/qcoreapplication.cpp:587
#35 0x00007fa6469b43e5 in QApplicationPrivate::sendMouseEvent (
    receiver=0x2299050, event=0x7fff50efabc0, 
    alienWidget=<value optimized out>, nativeWidget=0x2298960, 
    buttonDown=<value optimized out>, lastMouseReceiver=@0x7fa6473231a0)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:218
#36 0x00007fa646a1658c in QETWidget::translateMouseEvent (this=0x2298960, 
    event=<value optimized out>) at kernel/qapplication_x11.cpp:4133
#37 0x00007fa646a154f2 in QApplication::x11ProcessEvent (this=0x1fe0960, 
    event=0x7fff50efb330) at kernel/qapplication_x11.cpp:3255
#38 0x00007fa646a3b3c3 in x11EventSourceDispatch (s=0x1fed720, callback=0, 
    user_data=0x0) at kernel/qguieventdispatcher_glib.cpp:148
#39 0x00007fa6425160f2 in g_main_context_dispatch ()
   from /usr/lib/libglib-2.0.so.0
#40 0x00007fa642519396 in ?? () from /usr/lib/libglib-2.0.so.0
#41 0x00007fa64251982f in g_main_context_iteration ()
   from /usr/lib/libglib-2.0.so.0
#42 0x00007fa6476a3dff in QEventDispatcherGlib::processEvents (
    this=0x1fc0580, flags=<value optimized out>)
    at kernel/qeventdispatcher_glib.cpp:325
#43 0x00007fa646a3b20f in QGuiEventDispatcherGlib::processEvents (
    this=0x231f060, flags=<value optimized out>)
    at kernel/qguieventdispatcher_glib.cpp:204
#44 0x00007fa64767a055 in QEventLoop::processEvents (
    this=<value optimized out>, flags=@0x7fff50efb600)
    at kernel/qeventloop.cpp:149
#45 0x00007fa64767a1ab in QEventLoop::exec (this=0x7fff50efb640, 
    flags=@0x7fff50efb650) at kernel/qeventloop.cpp:200
#46 0x00007fa64767c1f9 in QCoreApplication::exec ()
    at kernel/qcoreapplication.cpp:845
#47 0x00007fa648aca36e in kdemain (argc=1, argv=0x7fff50efb9c8)
    at /tmp/buildd/kdebase-workspace-4.0.80/plasma/plasma/main.cpp:54
#48 0x00007fa64878f1c4 in __libc_start_main () from /lib/libc.so.6
#49 0x0000000000400629 in _start ()
#0  0x00007fa6488081d1 in nanosleep () from /lib/libc.so.6

Possibly related to http://bugs.kde.org/show_bug.cgi?id=162634 and/or http://bugs.kde.org/show_bug.cgi?id=161561