When you go to rebind select, when you press the new keybind it auto-inputs select again (or maybe I'm just not hitting the frame-perfect hit & release) and so it throws up the prompt to bind "select" again. Then you're trapped until you hit escape.
Similarly, when binding "back," it instantly takes you out of the keybind menu b/c the game thinks you're inputting "back" when you hit the key to bind it.