Application: umbrello (2.4.5)
KDE Platform Version: 4.4.5 (KDE 4.4.5)
Qt Version: 4.6.3
Operating System: Linux 2.6.32-trunk-amd64 x86_64
Distribution: Debian GNU/Linux testing (squeeze)

-- Information about the crash:
Created two classes. Filled one of the classes with 4 attributes, I hit the undo button to remove them and then redo to readd them, upon which the program crashed. 

The crash can be reproduced every time.

 -- Backtrace:
Application: Umbrello UML Modeller (umbrello), signal: Segmentation fault
The current source language is "auto; currently asm".
[KCrash Handler]
#5  0x000000000332b068 in ?? ()
#6  0x00007f7d49c35799 in QUndoCommand::redo() () from /usr/lib/libQtGui.so.4
#7  0x00007f7d49c36cf6 in QUndoStack::redo() () from /usr/lib/libQtGui.so.4
#8  0x00007f7d49c5a2a8 in QUndoStack::qt_metacall(QMetaObject::Call, int, void**) () from /usr/lib/libQtGui.so.4
#9  0x00007f7d490b7346 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/libQtCore.so.4
#10 0x00007f7d495ae132 in QAction::triggered(bool) () from /usr/lib/libQtGui.so.4
#11 0x00007f7d495b01ab in QAction::activate(QAction::ActionEvent) () from /usr/lib/libQtGui.so.4
#12 0x00007f7d4996a8ba in ?? () from /usr/lib/libQtGui.so.4
#13 0x00007f7d4996ab6c in QAbstractButton::mouseReleaseEvent(QMouseEvent*) () from /usr/lib/libQtGui.so.4
#14 0x00007f7d49a3710a in QToolButton::mouseReleaseEvent(QMouseEvent*) () from /usr/lib/libQtGui.so.4
#15 0x00007f7d4960a602 in QWidget::event(QEvent*) () from /usr/lib/libQtGui.so.4
#16 0x00007f7d495b432c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#17 0x00007f7d495bafdb in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#18 0x00007f7d4a9c6836 in KApplication::notify(QObject*, QEvent*) () from /usr/lib/libkdeui.so.5
#19 0x00007f7d490a415c in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQtCore.so.4
#20 0x00007f7d495ba1be in QApplicationPrivate::sendMouseEvent(QWidget*, QMouseEvent*, QWidget*, QWidget*, QWidget**, QPointer<QWidget>&, bool) () from /usr/lib/libQtGui.so.4
#21 0x00007f7d4963a03b in ?? () from /usr/lib/libQtGui.so.4
#22 0x00007f7d496389ac in QApplication::x11ProcessEvent(_XEvent*) () from /usr/lib/libQtGui.so.4
#23 0x00007f7d49664552 in ?? () from /usr/lib/libQtGui.so.4
#24 0x00007f7d4490b6c2 in g_main_context_dispatch () from /lib/libglib-2.0.so.0
#25 0x00007f7d4490f538 in ?? () from /lib/libglib-2.0.so.0
#26 0x00007f7d4490f6ec in g_main_context_iteration () from /lib/libglib-2.0.so.0
#27 0x00007f7d490cd713 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#28 0x00007f7d4966414e in ?? () from /usr/lib/libQtGui.so.4
#29 0x00007f7d490a2a82 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#30 0x00007f7d490a2e5c in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#31 0x00007f7d490a7aeb in QCoreApplication::exec() () from /usr/lib/libQtCore.so.4
#32 0x0000000000b6d1c5 in ?? ()
#33 0x00007f7d47f21c4d in __libc_start_main (main=<value optimized out>, argc=<value optimized out>, ubp_av=<value optimized out>, init=<value optimized out>, fini=<value optimized out>, 
    rtld_fini=<value optimized out>, stack_end=0x7fff071b37e8) at libc-start.c:228
#34 0x0000000000435769 in _start ()

Reported using DrKonqi