If you open up multiple levels of modal dialogs in FMP, and then switch to another application and back to FMP, the z-order of those modal dialogs gets reversed: the one that is supposed to be on 'top' (i.e. the last one opened) is buried behind the other dialogs. It won't come back to the front when clicked on, either. So if I open windows 1, then 2, and then 3, when I switch back to FMP window 1 will be on top, then 2 behind 1, and then 3 behind 2.
OS X 10.11.6
This happens in many different areas. An example few are:
Manage Database + field definition window (pictured below)
Manage Security + account definition + change PW window
You can still move the other dialogs off to the side to expose the one that is supposed to be on top; and the one on top still responds to button clicks and keyboard input as it should.