Well, I tried renaming each drive partition to something unique, but I'm still getting the same result - all mounted partitions are "selected" in the Startup Disk control panel, and I can't make any changes.

One thing I wonder - since each partition is on one drive, which has a single SCSI ID, perhaps that's what's causing the issue. I'm going to dig out an old external SCSI drive (with a different ID) and see if that makes any difference.

Thanks again for the help!

Huxley