One thing Ive found too (while animating).. when you parent thje dolly cam to the head for like a 1st person POV, Mine switched itself to a smaller percent on the scale (dolly cam "scale") . During the animation, the cam was moving , but falling behind....took me a bit to figure out why. cranked the scale on the cam back to 100 percent, then it fixed it.... FYI if it happens to you...