If all else fails just reset the whole unit and give it a reboot, you will need to redo speaker set up and all that but it may clear that glitch.
To reset entire unit (to be clear you will need to set the entire thing up again)
press on face plate "Multi" AND "speaker A/B" buttons AT THE SAME TIME and hold for 3 seconds.
To reset entire unit (to be clear you will need to set the entire thing up again)
press on face plate "Multi" AND "speaker A/B" buttons AT THE SAME TIME and hold for 3 seconds.