Hmm. Ok.
Then the only other option I can think of is the blizzppc asynchronous SCSI initialization crash. I found and reported the bug many many many moons ago. IIRC the triggering of the bug depended on timing, for example having a dummy 2nd HDD could delay the boot enough to hide the problem.
IIRC latest flashroms fixed the bug.
If it isn't this either, then I really have no clue.