When a menubar includes more items then possible to show, of course the menubar gets scrollable. Unfortunately the showMenuDialog(Dialog menu) does not take the Look and Feels vertical scroll width into account.
The result is that the vertical scrollbar overlaps the text.
I patched this behaviour with inheriting MyMenuBar from MenuBar, overriding showMenuDialog() and returning it in MyLookAndFeel:
The scrollbar width should be done in MenuBar.showMenuDialog(Dialog menu).