I have that happen when I use Keylight. If you are using keylight, instead of using the final result, try using the intermediate, seems to work better when I do that.
Another thing you can do is just take your “original” footage and drop it below the keyed footage-then just change the track matte of the original unkeyed footage to alpha matte.
Johnny Cuevas, Editor
Thinkck.com
“I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work.”
—THOMAS EDISON on inventing the light bulb.