I've had this twice over a few weeks now, and have noticed especially on a down shift the engine seems to stumble and bog coming back on the throttle. It's almost as if the engine is starved of fuel for a brief second. but doesn't come back from reving the engine but needs the clutch pulled in and a quick blip to right it self.

I've not checked for a while but the TPS was set to 17 I think, it has a PC5 fitted and side stand switch removed, K&N filter and otherwise stock. also a recent oil and plug change. it's a 2006 XTR.