Sounds like it could be a high speed stall.

Picture it this way. In a high speed turn, with a sharp bank angle, the lower wing will generate more lift than the high wing. If the high wing stalls at that point, the low wing is going to attempt to roll the plane to the right.

I wouldn't think the Sukhoi would do that though. Might want to check the wing and horzontal stab incidences.

Of course, I'm just guessing here. I could probably be more help if I saw it happen. :stupid:
Dennis-