I'm trying to anchor a mask along some footage, and each time I go back to check the flow the mask has moved slightly.

When I say slightly I mean if I'm using the arrow keys to move across and back over a frame it will look right going only one way. Come back across and it looks off. Go back the other way, and it's fixed.

But, when I render about 10 frames of test, it's off.

1. I have the keyframe timeline zoomed all the way IN.
2. I make sure the diamond has the focus so as not to edit the wrong frame.
3. I am saving often in this case.

Help!