Version: (using Devel)
Installed from: Compiled sources
While the apidox for KXMLGUIClient::plugActionList() explicitly says "You should not call createGUI() after calling this function. In fact, that would remove the newly added actionlists again..." this is just what happens if the toolbar gets edited and the changes saved. As a result all dynamically added menu entries are gone.
The solution to this problem is actually documented:
you should connect to the newToolBarConfig() signal and plug the action lists again in the slot; or do like KXmlGuiWindow::saveNewToolbarConfig() (which is the standard slot connected to that signal) and use removeClient+addClient again.
In fact, maybe your problem is already fixed? The fix was r803933 | dfaure | 2008-05-04, but maybe you were not using trunk when you reported this?
*** This bug has been marked as a duplicate of bug 64754 ***