UPDATE:

I spoke to Steve Demming this afternoon. He was a little skeptical at first, but over the phone we were able to recreate the memory loss and style volume control problems on his Tyros 4 as well. We were unable to attempt to recreate the sample problems because he had no samples installed on his board.

So unfortunately this looks like a Yamaha system issue.

I was disappointed to learn from Steve that Yamaha Japan takes its time getting back to Yamaha USA, so I hope these videos are somehow making their way to other countries as well.