hmmm....I have a 1/4 scale Extra 300s (13 lbs) that sorta does this also, only from the strart of a loop. If I pull to hard and hold it, it will start to look like a stop sign. Goes up a little and rolls to the right a little, goes up more, rolls more. Even if I pull moderatly it wants to roll to the right. If I make a very big loop it is much better.

CG dry is where the mfg recommends (Lanier) but wet (22oz) it would be nose heavy. Power is ST 2300, elevator servos are regular JR 42oz servo's. Throw's are less that mfg recommends.

Could I have a bad servo and stalling out, to nose heavy, or something else?