expected behavior
* minibuffer's message line is readable for the length of the width
of the emacs frame, modeline context menu offsets appropriately and
does not block minibuffer message line
Patches are welcome to pop up the menus so that they never overlap the
echo-area when tooltip-mode is nil. (This must be done up front, when
calculating where to pop up the menu.)
I do note that the most important use case where this comes into play,
which is menus on text-mode frames, already behaves that way. So the
problem is rather small and confined to a somewhat marginal use case.