Boots from PRO 860, but fails when I update the OS.

Customer brought in a Power Mac G5 with a failed HD, and for reasons decided to upgrade to an SSD. I put an Samsung PRO 860 inside, booted from a Leopard DVD, formatted the drive, and installed Leopard. No issues, and everything works fine. I then ran software update and it downloaded two updates, 10.5.8 and (I think) iTunes. When it restarted, it couldn’t find a bootable volume any more.

If I boot from the Leopard DVD it sees the volume as having 10.5.8 installed on it, and Startup Disk sees it as a viable boot volume. Holding OPTION at startup shows no bootable volumes (assuming the Leopard DVD has been removed).

I thought it might have been a bad install so I tried again with the same results: Under 10.5 it works fine, but after Software Update it breaks.

Some Googling around revealed that disabling TRIM may solve the issue so I removed the drive, put it in a PC, used Samsung Magician to disable TRIM (reformatting it in the process), put it back in the Mac, and tried again with the same results.

I tried it in both drive bays, same results.

Why can’t I boot this drive?

UPDATE: If I install 10.5, then update to 10.5.8, on a traditional spinning HD, then clone the resulting system to the SSD, the SSD boots and works normally. So it’s something to do with the update process itself that’s causing the issue.