I to am having the same problem, i am working on a fix for it, ill let you know what i find. i think it has something to do with the drivers/cat 9.11
Red2
ok so i rolled back my drivers to 8.632 before the "Boxy" problem went away however i am getting BAD frame rate drops that i started getting before the boxy problem but not before both IL@ ui 1.2 and cat 9.11 so i going to try rolling it back as well.
i also tried to go back to 9.10 that worked fine, so its probably mot a driver problem.
did you install il2 a second time before you got that problem.
cause i removed reg entry and the game more or less installed, then i got this problem with both installations...
EDIT: OK solved, just didnt uninstall 9.11 correctly. thank you for your answers and help