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.
What should I do then should I go back winging now or wait to see if they can get me some cash back first?
You could try getting a second opinion from another dealer. Alternatively, you need to make a bit of a nuisance of yourself and see what happens.