So, even if you disconnect every input except one, say DVD, it'll still switch to another input? Don't recall hearing of something like that before. To eliminate a wild theory about some strange random radiation affecting the remote receptor try covering the entire front of the receiver with some opaque object.

Even though you've already done a hard reset, if you didn't do so try the more basic unplug for a few minutes step.

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Enjoy the music, not the equipment.