Was your 800x800 version also 32bpc? It looks like your larger version is, although your project is set to 8bpc. What app are you generating the .tifs in? Can you check your framebuffer settings to see if there might be something there that's causing a conflict?
It might be just one file in the sequence that's flakey and it only shows up with reversal, because you may never have actually sampled the frame in normal mode. This might also have shown up during render only, e.g. when rendering with fields would have sampled the frames at a different time. I'd re-check your sequence. As ´TimeRemapper said, it may also be an issue with teh options you chose for saving the TIFFs. In that case running it through an image viewer/converter like XnView or Maya's fcheck utilty might fix the problems...
Mylenium you were right to guess that it was one corrupted tiff that was not initialy read while previewing the frames in the original order. To fix the issue I just had to re-render the frames which was a shame because I had to render the scene three different times to get a range of frames containing zero file corruption. TimeRemapper- I used Keyshot 3 to render the clown pass which is what you see here.
Thanks for the help guys!