Yeah, but this particular demo works fine in 3.1....as long as the fast ram is present. It is just odd how 3.1 applies all of the internal and trapdoor memory on the A500 to Chipram. You know, I tried to kick down to 1.3 and then boot workbench...and it only shows 512k of memory. I know that is off topic, but still kind of odd.
Basically, as soon as 3.1 was installed, all of the memory inside of the machine became chip memory, with no fastmem present. The demo must need some fastmem, which is why it only works with the SupraRam side expansion adapter in place.
I have another A500 and another 3.1 rom I will test tomorrow and see if it reacts in the same way.
EDIT: I think I have partially found my answer...from Wikipedia:
"All versions of the A500 could have the trap door RAM configured as Chip RAM by a simple hardware modification, which mainly involved fitting of a later model of AGNUS chip."
Apparently the 3.1 rom I had installed has "moved" my trapdoor ram to Chip ram without any other hardware modification otherwise. I did not replace the AGNUS however.