Hysteresis behavior...

I finally managed to get the latest firmware onto my machine. When I add an "m99 y.2" to the beginning of my code my parts come out "slanted" by about that much. I though this was a backlash compensation? Am I wrong, or using it in the wrong manner?

Additionally, an m98 does not return any non-zero values, but obviously something is changing because the part gets shifted, even with same gcode.

Any thoughts?