Sounds rather odd.
I've ran MacOS8.1 on my A1200 equipped with Blizzard 1230, and later on, on the same machine, with Blizzard 1260 together with a Mediator/Voodoo3. ShapeShifter had no problems whatsoever with the OS.
However, I did install it through Basilisk under Windows since my Amiga had no CD-Rom at the time. It was version 8.0 from CD, which I after the install updated to 8.1. I just moved the hardfile to my Amiga and voilá.
