Option Menu Can be Clicked on from Outside its Group

[Martin Blackman]

List,

If I make a group of 3 option menus, spaced out vertically, then I reduce
the group height so that only the top 2 menus can be seen, I can't click on
the 3rd option menu any more. So far so good.
But if I click on the 2nd option menu now, and its drop-down choices spill
over the bottom edge of the group, I am then able to click on the 3rd,
previously 'invisible' menu. Not good.
I have this situation in an application of mine using a scrolling group of
dropdown menus.   Seems like a bug to me, anyone care to confirm and or
suggest a fix ?

thanks
Martin