Okay I think I see what might have happened, is Backspace bound to any action?
This is the only case I've gotten it to behave as you explained, apparently I forgot to disable that as a key you can bind.. so this will be fixed as well.
To fix this you'd have to bind whatever action Backspace is bound to another key and then Backspace should behave as intended again.
And your expectation is correct, it's supposed to stay on the same screen and just set the action to "unbound".
That controller disconnection notification is normal, I'd have to rework aspects of my controller detection system to *maybe* get rid of that so that probably won't be fixed any time soon.
And yeah, you should probably wait for the next version, I'm on a bit of a break right now so I'll be getting back to work on this next monday.