Sometimes I find that when I add color correction to a clip, there will be a block on the video that does something weird. It could be just a little square block near the center of the screen or a rectangular block near the bottom of the screen.

What happens is that if I add any color correction, the block will go opposite. For instance, increasing gain, the block will get darker. Decreasing gain, the block will get lighter.

The block shows on the preview monitor on the computer screen and via firewire to my NTSC monitor. If I do a preview render to RAM, it still shows. But if I do a preview render to the hard drive, it does NOT show. It doesn't show in the final rendered project, either.

Is there a way to avoid this?

Thanks.