Hey Walter,
Thanks for your reply,
here is a box drawn with the rectangle tool on a clip, with a simple color layer offset underneath it.

do you see that line that goes across, at the top edge of the layer?
Now here is the same shot, nothing changed, except deleting the mask that is on the clip.

the line is gone, which leads me to believe that somehow, just a basic mask is causing some kind of transparency? Definitely not motion blur, nothing is moving. No effects are on it, no keying, no alpha. ideas? I tried this on a mac (I am on a pc) and did not see it happening.