I played it a bit (on an RX) and didn't have any issues with walking around and whatnot. If I messed around with the menu and character swapping, however, things happened. It wasn't consistent, and not all of them happened at the same time, but here's what I saw:
1) Characters could continue to move around with the menu open. That lead to them not following at the correct distance after the menu was closed.
2) Cycling through characters quickly caused a crash.
3) Going in and out of the menu, picking different options, caused a crash.
All in all, this is neat stuff and I hope you continue working on it. I particularly like the title screen birbs, the wading in the water transparency look, and the moving transparent red box; there's some definite potential here.