Pixelated frame image when keying for blue screen

I am rendering interview footage with two people in front of two keyed images. I shot all the footage 30fps on my Sony v1u. When rendering one of the keyed interview images is pixelating for one frame at seemingly random locations. The latest time it happened was when I put a title over it. Once i rendered the title, the keyed image pixelated for one frame. When I did clip disable, the frame pixelation went away. Here is a link to both images. i am editing on a octocore mac pro with a Radeon X1600 graphics card adn 4gb of ram.

[www.jimfinn.org]

Thanks, jim finn

....need more info. What are your sequence / render settings? Capture settings? What is the format?

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