We had one client who was attempting to restore a backup (I think they were self hosted and had been trying things beyond their knowledge level 
) , and we had another client who asked us to set up a staging site for custom plugin development purposes and we took a backup from CDCK hosting.
in general the built in versioning mechanism in the backup metadata works really well in being able to proactively determine when something is going to blow up or not, but these kind of situations* are like land mines 
(* Actually, the only other thing I can think of that is not covered by migration versioning is when a migration with an older date stamp is injected into main, but I digress)