Transmission continued to rev while in neutral...

[MyATLz]

I have no mods and about 3000 miles on the car. It is the sport model 6 speed manual so it has the synchro rev match.

This has happened twice at random times. Car was running fine both times. Then I pull up to a stop light after downshifting. Then I place the car in neutral and it will sit at 2000 rpms. Then it will continue to rev. In the 2nd instance it got up to 3000 rpms before I put the car in 2nd gear and left the stop light. After moving the revs go back to normal. Then it happens again at the next stop light. Finally I get to my destination and turn off the car. I start the car up again about 15 minutes later and everything is back to normal.

Any ideas, suggestions? I am guessing if it doesn't happen all the time it's not that big of a deal. And if the people at Nissan can't replicate it when I take it to the dealer they won't do anything anyways.

EDIT: I guess I should have made the title more clear. Obviously it will rev while in neutral. What I meant is that the revs stayed high and continued to get higher.