I have configured my CFFA card with five ProDOS volumes, based on a bug report for something that I wrote.
On my system, ProDOS maps two volumes at slot 7, two at slot 4, and the final one at slot 1.
If I ask ProDOS to do a block read of the unit in slot 1, it succeeds and I see the expected content.
If I try to do the same thing without ProDOS (by calling $C70D with the exact unit number), I get garbage being read.
If I iterate through all unit numbers and then dump the volume names, I see all of the volumes other than the one in slot 1.
i.e. I can read any volume successfully other than the one in slot 1.
I didn't see anything in the firmware disassembly that would suggest special handling for ProDOS but I might have missed it.
Any idea what else could be the cause?