Well, I can't say much from the Amiga side, but after playing around with
Macs for a number of years, I don't think there were really any instances
where instructions were _removed_ that broke software... I do remember
there were a few specific issues when features were _added_ and a lot of
software broke, like when the 68020 macs were introduced with onboard
caches that broke some software that used self-modifying code, and when
the 68040 was introduced with its onboard caches, I think it ended up
breaking some software as well. This is all mac-related stuff, though,
so I don't know if there were ever any similar issues over on the Amiga
side.
-Sean Caron (root(a)diablonet.net)