Version:           1.5.6 (using KDE KDE 3.5.5)
Installed from:    Fedora RPMs
Compiler:          gcc, I think... ( whatever ships with FC6 ) 
OS:                Linux

To reproduce:
Create a new activity diagram, create a start and two activities.  Try to add a transition from one activity to the next.  It crashed, for me:

(no debugging symbols found)
Using host libthread_db library "/lib/libthread_db.so.1".
(no debugging symbols found)
...
(no debugging symbols found)
[Thread debugging using libthread_db enabled]
[New Thread -1208669504 (LWP 18712)]
(no debugging symbols found)
...
(no debugging symbols found)
[KCrash handler]
#6  0x081d1079 in UMLObject::setUMLPackage ()
#7  0x08195b22 in ToolBarStateAssociation::addAssociationInViewAndDoc ()
#8  0x08195d77 in ToolBarStateAssociation::setSecondWidget ()
#9  0x08194684 in ToolBarState::mouseRelease ()
#10 0x486438e1 in QScrollView::viewportMouseReleaseEvent ()
   from /usr/lib/qt-3.3/lib/libqt-mt.so.3
#11 0x486413af in QScrollView::eventFilter ()
   from /usr/lib/qt-3.3/lib/libqt-mt.so.3
#12 0x4851322c in QObject::activate_filters ()
   from /usr/lib/qt-3.3/lib/libqt-mt.so.3
#13 0x485132ab in QObject::event () from /usr/lib/qt-3.3/lib/libqt-mt.so.3
#14 0x48550cfc in QWidget::event () from /usr/lib/qt-3.3/lib/libqt-mt.so.3
#15 0x484aae6b in QApplication::internalNotify ()
   from /usr/lib/qt-3.3/lib/libqt-mt.so.3
#16 0x484ac4c7 in QApplication::notify ()
   from /usr/lib/qt-3.3/lib/libqt-mt.so.3
#17 0x47c9ad82 in KApplication::notify () from /usr/lib/libkdecore.so.4
#18 0x484429c6 in QETWidget::translateMouseEvent ()
   from /usr/lib/qt-3.3/lib/libqt-mt.so.3
#19 0x484414c6 in QApplication::x11ProcessEvent ()
   from /usr/lib/qt-3.3/lib/libqt-mt.so.3
#20 0x4845314b in QEventLoop::processEvents ()
   from /usr/lib/qt-3.3/lib/libqt-mt.so.3
#21 0x484c43f0 in QEventLoop::enterLoop ()
   from /usr/lib/qt-3.3/lib/libqt-mt.so.3
#22 0x484c42a6 in QEventLoop::exec () from /usr/lib/qt-3.3/lib/libqt-mt.so.3
#23 0x484aa97f in QApplication::exec () from /usr/lib/qt-3.3/lib/libqt-mt.so.3
#24 0x0816ac5c in main ()