Ahh, I remember that glitch. Twas so funny yet sad to see users bodies getting switched about,
Lol.
I believe that usually occurs whenever this glitch ends up happening where another user is inside someone else. ( i.e User A is inside / controlling User B ).
I must admit though, it has been awhile since that's happened, even after returning from my Hiatus. Lol.
So unless that changed, that's usually what happened whenever I encountered it.. Happened to me once before c':