RE: my new sig sundancer
May sound like stubid advice but have you checked your incidence meter up against a level or something?
Ive done quite a few bipes and if thrust line, CG, wieght, are the same. I would normally suspect that the top wing would have a positive incidence over the lower with that kind of behavior. Zero the lower with the stab and then set the upper to -1/2*-1* no more. Yeah its a shot in the dark but its worked for me in the past. Other than that I too would be clueless as to what is going on.