I'm thinking that an adverse rudder angle and lateral balance problem may be the cause.
I took all of the right thrust out of mine when I put in a TT 91 FS and it flies just great. Hmmm...
Haven't flown it in a while but I'll definately be watching for right side fall-off when going vertical.
It would seem that it is true that a nose heavy plane flies stoically and will live to see another day while a tail heavy plane generally flies once!

The retracts can be smoothed out a bit for landing and take-offs. See the Tips & Techniques forum for ideas. It may take some searching...

Good luck,
Jeff