mouse@Rodents.Montreal.QC.CA said:
> But when I use a 1.4-based kernel, I get "pckbdprobe: reset response
> 0xfc" and the keyboard doesn't work. 

As you found, nothing which could explain this was changed in
the keyboard or keyboard controller drivers.
I'd suspect a subtle timing related problem because the
i386 DELAY() implementation was changed within the timeframe
in question. DELAY()s are supposed to be more accurate now which
probably means that the real time got shorter for small delays.
You could try to inclease the delay constants in dev/isa/pckbc.c,
especially KBD_DELAY. If this doesn't help: there are some
loop constants within this file which you could play with.

best regards
Matthias