PS/2 memory problems (was: Re: AIX for PS/2?)

To recap, I found a PS/2 model 65sx with 6MB of RAM via an on-board 2MB and 4MB SIMM (no additional memory boards). POST would pass the RAM, but then cough up 161 and 163 errors due to a dead Dallas module battery. I grafted a new battery into the Dallas module, which cleared the 161 and 163 errors - but then POST suddenly started throwing up 203 and 201 memory faults (along with error locations). Playing around with swapping the two SIMMs around and booting with just one in either of the two sockets seemed to suggest that the 2MB module had gone bad; with just the 4MB module in either of the two system board sockets, I'd get "00640 KB OK" and a 201 error, but no error location. Assuming (incorrectly?) that the 201 was now due to the system not having the amount of memory it expected, I booted from the reference disk and did an automatic configuration (as suggested by the software when RAM had been changed). That said all was well and that I should reboot, which I did - at which point POST would count up to ~3700KB[1], overwrite with "400000 FFFE 201", clear the screen and show "3712 KB OK" along with a 201 and 164 error. [1] the overwrite happens so fast that I can't read the exact number, although it seems sensible to assume that it's actually 3712. Two things puzzle me: 1) Two SIMMs going bad at once seems unlikely (although not impossible, of course), 2) I can boot the reference disk, and the system shows that it has 4MB of RAM, and when the self-tests are run it passes the memory just fine. I suppose it's possible that the 3712 figure is correct, given that the techref for the 65sx talks about reserving 128KB for video memory, 128KB for system ROM and 128KB for I/O ROM - but it doesn't explain why I'm getting that "400000 FFFE 201" message and 164 error. It's almost as though it's forgetting across reboots that it just has 4MB now, and so it barfs when it tries to count beyond the 4MB boundary. Anyone able to shed any light on this?