Thanks for the reply.
It was originally a .mts file, shot full HD on a Panny AF-101, but in accordance with Dave LaRondes rule #1, I converted it down to a PAL Widescreen Quicktime, animation codec, before putting it into AE. Im trying to render it out in the same format. Like I said, Camera tracking effect on, background film has a shite render. Effect turned off, everything is ok. I mean its not the end of the world, and its an easy, simple workaround. I was just wondering if anyone else had experienced something similar…