not sure what happened, but when two of my drives stopped mounting in Windows from my Linux server (don't know why), JRiver removed every file in the library from those drives.
I added the drives back, restarted MC, but the files did not re-appear in the library. Had to rescan them all back in.
I've not seen this behavior before; does MC auto-clean the library if a drive disappears now or is there a setting that controls this type of behavior? Obviously the root cause of the problem is why did the drives stop mounting in the first place, but I still surprised I lost all the content on the drives in MC's library.