We had multiple problems with our MDE accounts, and when the CM was trying to fix it, my Mother's ticket disappeared into the Disney IT blackhole. The CM told us to just readd the ticket that disappeared and all would be well.
When we put the ticket numbers in, we were told that the ticket was "already assigned to someone else, and could not be added again." A special Disney IT group had to be called in to fix this problem.
I suspect that once any ticket is added to MDE, you would run into the same problem of being told that the ticket wasn't valid for anyone else, and that is why they aren't returnable.