Well, apparently the stupid mount edits the ISO file for some reason:
http://unix.stackexchange.com/questions/149459/mount-o-loop-changes-mounted-iso-image-file
If I had just run the command with a “ro,” in there before the “loop”, all would have been fine.
If that’s the case then the ISO definitely wasn’t corrupted - it’s just a slight different .iso file with all the same contents. So it did not cause the glitches Blackout had.