Fullscreen + TUIK dropdownbtn = strange flicker

I am getting a strange flicker issue with my performance window. Run the TOE in the attached zipfile and then click any down arrow or dropdown list and you should see the screen flicker black.

flakeD.041.zip (204 KB)
If I have the perform Window COMP set to:
Fill Area=On
Borders=Off
then I get flicker when opening a dropdown list, if I change either of those settings, the flicker goes away. The dropdowns are all TUIK list components.

There must be something else at play though, because I tried to create a simple test case with just a window comp and a dropdownbtn comp and it didn’t flicker.

Any ideas? For now I’ll just resize my window and run in bordered mode, but I do think that fullscreen looks nicer in general.