clutch arm raises at high rpms

my clutch arm(not the hand lever) raises up when i hit the powerband and around there. when i push it all the way down, it is protruding about a half inch out of the case. if i keep it under about three-quarter throttle it doesnt seem to raise out, but if i go any higher it comes up about a half inch and no more. it doesnt feel any different or shift any different from what i can tell, but its annoying at the least!

im thinking there might a big build-up of pressure in the case when i hit the powerband, so its relieving pressure in any way it can, hence pushing out the arm as much as it can.
i know the crank vent tube isnt blocked all the way but it could be partially, i havnt checked yet though.

any ideas???