I've noticed some strange behavior with the actions tab in the AD&D ruleset. It's a very "busy" window with tabs/window/subwindows/scrollbars and various other things. That window appears to have some display issues under FGU.
Here is an example of what it looks like in FGC.
https://i.imgur.com/DDz7PET.gif
And here is how it works in FGU.
https://i.imgur.com/3oPUe4N.gif