OS X Combobox Top-Level Display

I have a combobox in a window, and I’m running this on OS X. When I
click
on the dialog button to drop it down, the toplevel that displays the
list is
behind the window (in this instance, the root window), and I have to
click
on the overhanging part to make it come forward. This can be an issue
for
users when there is no overhang, however (as they may not know that just
moving the window containing the combobox will reveal the list window).

Any resolution?

Thank you.

~Matthew Maycock