I still can reproduce with b6 version. Do this:
Press 3 or 4 in ECS/AGA Games screen
Reboot Amiga/WinUAE or exit with Escape if you have loop in s-s like me to run TL until F10 pressed.
While TinyLauncher launch again press few time (2 or 3 is almost everytime enough) F5 key while monster picture is bouncing and you should see AGAGA text. Probable it is a reason that two screens lay on themself somehow. But you must check. Cut from my *.hdf with Tiny Launcher of S:startup-sequence file looks like below (ah, the same bug is on real Amiga 1200):
set >NIL: Reply `DH0:TINYLAUNCHER/TinyLauncher.exe`
IF $Reply not eq "5"
skip LOADTL BACK