I don't know why this happens, but here's a couple of things you might try.

To reset the amp screen, try this procedure. The procedure in the manual usually works, but on mine it also deletes all of the timer settings, so I use this one also.

Commander off/Component key (Amp, in this case)
Press and hold DEL at top of the screen
Press Component name (Amp) to the right of the DEL key

This should clear the key. If not, the complete reset is the only other option, which is a real bummer.

Try learning the right arrow key on an unused screen before you do the complete reset, if required, and see what happens. Also, try using a short press of the key. Sometimes certain commands will react in a different way to different learning procedures.