My bike has just started doing this twice in the past week. Normally when i press the starter buttom it will rev up to 2000 rpm then come back down to 1500 rpm. It has started to rev to 2000 then increase to 4500 5000 and i blip the throttle and it comes back down to 1500 rpm. My bike is 6 months old with 3000 kilometres on the clock. Its summer here and outside temperature was 33 degrees when it done it today so its nothing to do with the bike revving more because of the cold temperature.
I also agree that when I take it back to my Honda dealer they will find nothing wrong with it.