HI!
That shouldn't be the case, no. I just tested it and it does change to a new character every time, so IDK what's the issue with that.
When removing a FANGAN from the roster, you just remove all of it's characters from being the potential solution, but since you change the number of characters, it does change the solution character, so thats just a bug out of a feature. I'll be looking into that, since that wasn't a bug during the tests :/
Also Thanks :D