Missing update (in QMenuBar?)

Qt seesm to fail to update parts of the menubar in some cases.

This is not reproducible, but I've seen similar effects in other Qt 4.7 based applications.

The "misdrawing" persist when simply moving the main window around.

In this particular instance it went away when 'Alt' was pressed which might have triggered an update.
In any case I'd take this as an indication that it's not a WM problem as the WM does not act itself on
plain 'Alt'.

In similar cases, the foreground of QLineEdits gets painted black (actually it looks like the bounding
boxes of the glyphs making up the contents of the line edit, so it's some kind of "ragged black bar").
This is "fixable" by selecting the contents of the line edit, but comes back as soon as another letter
is typed.