[bug?] other player champion in my soverign stack?

I was standing guard outside the wild-lands, waiting to upgrade my armor & weapons, so I could hit elite threat and suddenly found a hero from another faction in my stack.  I moved the stack, thinking it was just passing through, but it came along with my stack.  Is this a new feature, other players hero's tagging along to get exp points from my battles?  It wasn't the leader, just one of the champions for hire, a baseline one, to boot, no experience.

EDIT:  Great, I saved to make this post, now I ctd when I try to load that save game to see what happens.  Any clues to load bad saves?

EDIT2:  Rats, now there's .77?  This error was from .76, let me patch.

EDIT3:  Nope, .77 will not load that save, either.  I really wanted to play that save to see what happens with the foreign hero.