Vray camera distortion animation is flakey

[stevesideas]

Im having real problems when trying to animate distortion on the vray camera. I was using a standard max camera and trying to animate the camera mod that sorts the verticals but that wasnt working at all. The vray camera distortion doesnt seem to be much better. In the viewport the verticals suddenly flick from correct to none as I scrub the timeline.

Any ideas what I should do ?