Hi lionstorm,
I got some answers that it should work (at least what I heard) and the 0.5 release got a special release for OS4 which fixed a problem with the Icon.
But as always the disclaimer... I do not have an OS4 computer so I can't really try and in UAE it seems to work as you see:
What you can try:
Delete/rename the Icon, start from shell maybe that will work? do you have MUI installed? of course it needs MUI (my UAE has MUI 3.9 default). Did you check the error console for any errors, I don't know how to access that in OS4, but there should be a way.
Did you try the 68k Version?