Menu problem on Mac

I've got a menu working on my site, having started with version 3.5 and now
adapted to 5RC3.  With version 3.5 I had a big problem with IE on Mac OSx
where the menu would show only a few pixels wide and would jump down and
display submenus much lower on the page than the main menu.  Therefore I
upgraded to the beta version 5RC3 and now it works fine with all PC and Mac
browsers I have tested (including Safari) but on IE for Mac under OSx there
is still a problem.  The menu appears, and even works, but it will jump down
from its original position to a new position about 50 pixels lower on the
page.  This happens when the cursor first rolls over any menu item, and it
stays there and works fine from then on.  Sometimes (but not always) a
refresh will start it out at the higher location again, and then it will
jump down when touched.  The URL for my site is http://www.cyso.us and I
would appreciate any advice or test results from the group.

As a guess, I'd say that the problem is with the code that moves the menu
down slightly when a border is added to an item.  On Safari I can see all of
the items below move down slightly (a few pixels), although that doesn't
happen with IE on Windows.  However, with IE on the Mac the whole menu moves
down.  Maybe this is a bug in IE?  Is there a workaround?

Thanks!