PR2 tilt oplev P and Y started crazy when (or, after) the X arm engaged resonance... 

By the way, have this trend-oscillation also been obeserved when you did not do the dithering of PR2? (for example, the dithering freq is too high for PR2???)

In case this happens every time the cavity is aligned, this might be due to some ghost beams by the light source of the oplev itself, for example + unfortunately (as you may know, no cares for those ghosts there, as far as I know), although such big changes were not observred in the trend of tilt-SUM and len-SUM; even a fraction of light might be enough to rise "pitch and yaw signals" even though it won't change the SUM so much.