I had a new Roland E-70 many, many moons ago, that would lock the left hand sound on the last chord played, with the new chord only changing thew style. It was totally a random thing. The only way to stop it, was turning the instrument off, and back on. I was working at a music store in Newfoundland, so I sent the keyboard back to Roland Canada, and it was replaced with a new one. The second one worked perfectly.

This was in the days before OS upgrades could be user installed.

Outstanding service by Roland Canada, but at the time, the glitch was very irritating, as are all random problems.

I hope this issue with Dave's PA-900 can be rectified as soon as possible, as, like Donny said, it doesn't give you a very secure feeling knowing it can happen at any time.

Ian