I think it's suspicious that only the sound cuts OFF, but the receiver itself is still ON. So the power is still on, but there is just no sound.
Normally, when you short-circuit (bare wires touching, etc.), the entire receiver shuts OFF. That has happened to me before - bare wires touching.
If you are using the "A" speaker posts, try using the "B" speaker posts instead and see if it still does that.
Also try to do a HARD RESET on your receiver (check manual). On mine, I have to push a few buttons simultaneously. I can't remember which buttons though.