Awesome research into the issue! I'll certainly do what I can to help. I _think_ I'm at the point of interest in the source but it's almost like reading pure disassembly - not a lot of help gained from labels, variables etc. So, with some uncertainty, the check is simple whether it was able to read a volume or not from the disk. If it did, it's shown. If not, it continues on.
There's also some logic around a forced mediachange that I'm trying to follow. I'll try to put some time into understanding it.
/Troed