What were you doing when the application crashed?
If 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? 
You need to install the "kdesdk-debuginfo" package
Thanks

Hi,

I don't know if this bug is the same but it happens when I delete an action in the "Command History". KDE 4.2.4 from Debian sid.

Backtrace:
Application: Umbrello UML Modeller (umbrello), signal SIGSEGV
0x00007f15b5045800 in __nanosleep_nocancel () from /lib/libc.so.6
Current language:  auto; currently c

Thread 1 (Thread 0x7f15b906c760 (LWP 21034)):
[KCrash Handler]
#5  0x0000000001c6045a in ?? ()
#6  0x00007f15b6c37a22 in QUndoStack::setIndex (this=<value optimized out>, idx=2) at util/qundostack.cpp:740
#7  0x00007f15b6c38e1f in QUndoModel::qt_metacall (this=0x1b11680, _c=QMetaObject::InvokeMetaMethod, _id=29754384, _a=0x7fffc11aa9b0) at .moc/release-shared/qundoview.moc:73
#8  0x00007f15b613c862 in QMetaObject::activate (sender=0x1ceb990, from_signal_index=<value optimized out>, to_signal_index=5, argv=0x2024630) at kernel/qobject.cpp:3120
#9  0x00007f15b6b5dd8a in QItemSelectionModel::currentChanged (this=0x2014790, _t1=<value optimized out>, _t2=<value optimized out>) at .moc/release-shared/moc_qitemselectionmodel.cpp:153
#10 0x00007f15b6b5ded4 in QItemSelectionModel::setCurrentIndex (this=0x1ceb990, index=<value optimized out>, command={i = -1055216688}) at itemviews/qitemselectionmodel.cpp:1123
#11 0x00007f15b6b12980 in QAbstractItemView::mousePressEvent (this=0x1ce8140, event=0x7fffc11ab8e0) at itemviews/qabstractitemview.cpp:1509
#12 0x00007f15b6646926 in QWidget::event (this=0x1ce8140, event=0x7fffc11ab8e0) at kernel/qwidget.cpp:7517
#13 0x00007f15b69e283b in QFrame::event (this=0x1ce8140, e=0x7fffc11ab8e0) at widgets/qframe.cpp:559
#14 0x00007f15b6b1796d in QAbstractItemView::viewportEvent (this=0x1ce8140, event=0x7fffc11ab8e0) at itemviews/qabstractitemview.cpp:1471
#15 0x00007f15b6126158 in QCoreApplicationPrivate::sendThroughObjectEventFilters (this=<value optimized out>, receiver=0x1ce9110, event=0x7fffc11ab8e0) at kernel/qcoreapplication.cpp:726
#16 0x00007f15b65f54cc in QApplicationPrivate::notify_helper (this=0x19fff70, receiver=0x1ce9110, e=0x7fffc11ab8e0) at kernel/qapplication.cpp:4053
#17 0x00007f15b65fdeda in QApplication::notify (this=<value optimized out>, receiver=0x1ce9110, e=0x7fffc11ab8e0) at kernel/qapplication.cpp:3759
#18 0x00007f15b7b9338b in KApplication::notify (this=0x7fffc11ad670, receiver=0x1ce9110, event=0x7fffc11ab8e0) at ../../kdeui/kernel/kapplication.cpp:307
#19 0x00007f15b6126e4c in QCoreApplication::notifyInternal (this=0x7fffc11ad670, receiver=0x1ce9110, event=0x7fffc11ab8e0) at kernel/qcoreapplication.cpp:610
#20 0x00007f15b65fd128 in QApplicationPrivate::sendMouseEvent (receiver=0x1ce9110, event=0x7fffc11ab8e0, alienWidget=0x1ce9110, nativeWidget=0x1ad16e0, buttonDown=<value optimized out>,
    lastMouseReceiver=@0x7f15b705fc30) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:216
#21 0x00007f15b6667009 in QETWidget::translateMouseEvent (this=0x1ad16e0, event=<value optimized out>) at kernel/qapplication_x11.cpp:4448
#22 0x00007f15b6665d4d in QApplication::x11ProcessEvent (this=0x7fffc11ad670, event=0x7fffc11ad2b0) at kernel/qapplication_x11.cpp:3566
#23 0x00007f15b668e4d4 in x11EventSourceDispatch (s=0x1a03bc0, callback=0, user_data=0x0) at kernel/qguieventdispatcher_glib.cpp:146
#24 0x00007f15b195cf7a in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#25 0x00007f15b1960640 in ?? () from /usr/lib/libglib-2.0.so.0
#26 0x00007f15b19607dc in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#27 0x00007f15b61504bf in QEventDispatcherGlib::processEvents (this=0x19ec270, flags=<value optimized out>) at kernel/qeventdispatcher_glib.cpp:324
#28 0x00007f15b668dc7f in QGuiEventDispatcherGlib::processEvents (this=0x2014790, flags=<value optimized out>) at kernel/qguieventdispatcher_glib.cpp:202
#29 0x00007f15b61256f2 in QEventLoop::processEvents (this=<value optimized out>, flags={i = -1055205984}) at kernel/qeventloop.cpp:149
#30 0x00007f15b6125abd in QEventLoop::exec (this=0x7fffc11ad5e0, flags={i = -1055205904}) at kernel/qeventloop.cpp:200
#31 0x00007f15b6127d84 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:888
#32 0x0000000000bab405 in main (argc=3, argv=0x7fffc11ada98) at ../../../umbrello/umbrello/main.cpp:110


GDB output:
(gdb) run
Starting program: /usr/bin/umbrello
[Thread debugging using libthread_db enabled]
[New Thread 0x7f1378607760 (LWP 21398)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7f1378607760 (LWP 21398)]
0x0000000000c638ad in UMLWidgetController::insertSaveValues (this=0x20596b0, _oldX=134, _oldY=326, X=146, Y=338) at ../../../umbrello/umbrello/umlwidgetcontroller.cpp:400
400     ../../../umbrello/umbrello/umlwidgetcontroller.cpp: No such file or directory.
        in ../../../umbrello/umbrello/umlwidgetcontroller.cpp

@Vicenç Juan Tomas Monserrat: your crash is like bug 174397. Thanks