I did the firmware update as you recommended and it works! Here's the reason's I did not do this in the first place:
1) Assumption that when the Apple Genius personnel performed the 5.1.5 firmware update (which I watched them do) for me 3 weeks ago that they did this very update - bad...
My single processor 1.8 Ghz Power Mac G5 will not deep sleep after s/w update from Apple. It will deep sleep after an archive reinstall of the original Panther family pack (OS X 10.3), but it no longer deep sleeps after s/w update to 10.3.9.
Symptoms after going to sleep:
1) Fans stay on...
My 1.8 single G5 won't go to full sleep mode. The monitor and Ethernet go down, but the fans keep spinning. The sleep light stays on. I suspect other things don't power down (maybe disks).
After doing archive reinstall this problem is fixed, but eventually comes back again after SW...