I also have the same issue, mine has only affected the game setting so far, but have also since lost the onscreen display. Which has really annoyed me! Was thinking of upgrading to the 608 or even the 808, but now have second thoughts for fear of the same thing happening again.
Since I cannot find my receipt does anyone know if this will cause issues when contacting Onkyo to try and get the issue sorted? Mine is also around 2yrs old.