Boot from Apple Partition Map
 

I didn't think this was possible, but user has drive partitioned as Apple Partition Mac with Time Machine and SuperDuper clone that boots. I thought you had to be formatted as GUID to boot. How is this possible?

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It doesn't show up in the Startup Disk preference pane, though, does it?

Yes, it does show up in System Preferences > Startup pane. Check the screen shot. I was screen sharing and was able to see him boot into the drive.

Sorry, didn't see the screen shot. Can't explain it: I've just checked that APM does not appear for me. Weird.