Jimbo,
Mine does it too.............but it shouldn't happen. My local dealer said If I wanted it investigated further, I would have to pay for a new clutch if they looked at it and if the gearbox was thought to be faulty, I would have to pay for a replacement up front and they would then approach Nissan for a refund under warranty but could not confirm they would cough up. I will do the job myself when it gets that bad and put a half decent clutch (Sach's) in, thrust bearing (which if you ask me is half of the problem) and pressure plate in.
Best of luck with it. Feel for you.