Mocha track perfect in AE precomp, slips in other comp

I can’t for the life of me figure this out. Perhaps one of you have run into this? I have a rock solid corner pin track in Mocha. I’m using Red Giant Corner Pin and everything looks perfect in AE in my precomp. But when I take that precomp into another comp, the track is noticeably slipping. It’s like the timing is off by a fraction of a frame. Sliding the corner pin layer one frame either way in the timeline doesn’t fix the problem.
Everything is the same frame rate, resolution, square pixels, etc. Any idea what is going on here? I can’t figure it out for the life of me. The only thing I can think of is to pre-render the precomp. But I’d still like to know what the heck is going on.
(Keep in mind that Precomp A means the entire frame that contains a person and the corner pinned layer, not just the corner pinned layer itself).
Image: http://i175.photobucket.com/albums/w134/navstar/Screen-shot-2011-07-25-at-21257-PM.png
Image: http://i175.photobucket.com/albums/w134/navstar/Screen-shot-2011-07-25-at-21307-PM.png

Are the frame rates of your various comps and precomps matching the frame rate of the mocha file? It could also be an aspect ratio problem, or a transform affecting your corner pin. It’s hard to tell what it is without troubleshooting the file.
Cheers,
Mary

Is there a transform on the precomp? Or a null attached? Like I said, it’s hard to diagnose without seeing the file. You can upload the project files to me if you like, I can email you the ftp info.
Cheers,
Mary

Yes, everything is the same. Square pixel, 23.976, same resolution. But again, it’s perfect in the precomp. Why would it shift??