Version:            (using KDE Devel)
Installed from:    Compiled sources
Compiler:          gcc 3.3.3 
OS:          Linux

Create 2 classes, class1 and class2. Create an operation in each class, say class1_method() and class2_method(). Cut class2_method from class2 using the context menu, and paste it into class1. The cut and paste doesn't work (with error message: "umbrello: WARNING: UMLListView::popupMenuSel called with unknown type"), and the method shows up at the bottom of the list view, outside the tree hierarchy. 
If you then try and cut the method from there (i.e., the bottom of the list view), umbrello crashes. Here's the backtrace:

#0  UMLObject::getBaseType (this=0x0) at umlobject.cpp:204
#1  0x081723e8 in UMLListView::popupMenuSel (this=0x8386f00, sel=1972)
    at umllistview.cpp:298
#2  0x08176701 in UMLListView::slotCutSuccessful (this=0x8386f00)
    at umllistview.cpp:1586
#3  0x0817b2c6 in UMLListView::qt_invoke (this=0x8386f00, _id=121, 
    _o=0xbfffe9d0) at umllistview.moc:204
#4  0x40be3d16 in QObject::activate_signal () from /usr/lib/libqt-mt.so.3
#5  0x40be3bd4 in QObject::activate_signal () from /usr/lib/libqt-mt.so.3
#6  0x0815e9ed in UMLApp::sigCutSuccessful (this=0x0) at qmetaobject.h:261
#7  0x0815ad75 in UMLApp::slotEditCut (this=0x831cea0) at uml.cpp:742
#8  0x081725f9 in UMLListView::popupMenuSel (this=0x8386f00, sel=1976)
    at umllistview.cpp:363
#9  0x0817b247 in UMLListView::qt_invoke (this=0x8386f00, _id=115, 
    _o=0xbfffede0) at qucom_p.h:388
#10 0x40be3d9c in QObject::activate_signal () from /usr/lib/libqt-mt.so.3
#11 0x40be3efd in QObject::activate_signal () from /usr/lib/libqt-mt.so.3
#12 0x40f16862 in QPopupMenu::activated () from /usr/lib/libqt-mt.so.3
#13 0x40ce068c in QPopupMenu::actSig () from /usr/lib/libqt-mt.so.3
#14 0x40ce4ad6 in QPopupMenu::mouseReleaseEvent () from /usr/lib/libqt-mt.so.3
#15 0x40c18da7 in QWidget::event () from /usr/lib/libqt-mt.so.3
#16 0x40b8847f in QApplication::internalNotify () from /usr/lib/libqt-mt.so.3
#17 0x40b87b81 in QApplication::notify () from /usr/lib/libqt-mt.so.3
#18 0x4077db29 in KApplication::notify () from /usr/lib/libkdecore.so.4
#19 0x40b1fee1 in QETWidget::translateMouseEvent ()
   from /usr/lib/libqt-mt.so.3
#20 0x40b1de12 in QApplication::x11ProcessEvent () from /usr/lib/libqt-mt.so.3
#21 0x40b33f01 in QEventLoop::processEvents () from /usr/lib/libqt-mt.so.3
#22 0x40b9bce8 in QEventLoop::enterLoop () from /usr/lib/libqt-mt.so.3
#23 0x40b9bb98 in QEventLoop::exec () from /usr/lib/libqt-mt.so.3
#24 0x40b886d1 in QApplication::exec () from /usr/lib/libqt-mt.so.3
#25 0x0813e464 in main (argc=0, argv=0x0) at main.cpp:86


As a final note: using drag&drop to move an operation between classes does nothing, which is not what you'd expect.