your causing it to Snap
Outside Snap roll is Down elevator and opposite aileron and rudder......I bet your getting a little snap type action when rolling from inverted you should be giving top rudder...when rolling right from inverted is right rudder. If it slow it down you a little heavy on it perhaps and stalling things out...try a little blip of power and less rudder.
But I think it might be snapping that 1/2 roll from inverted with the imputs you describe....
give her a shot. Thats the great thing about this sport its all about learning new stuff.
Troy Newman
Team JR