visible area of a dropdown menu

[Chris Phillips <chris thirtythreeandathird net>]

Hi, i've got an OptionMenu which is working correctly and all, but it 
doesn't seem to draw correctly....

http://thirtythreeandathird.net/dropdown.png

As you can see (if indeed you can...) it only draws on the first half of 
the space allocated to it, the remainder being blank and looking awful. 
This is just using dumb MenuItems, nothing fancy at all. Can anyone say 
why this is appearing this way??

thanks

Chris