Hasta La Motion!

I have a little question. When using the Lens Distortion tools, undistort my plate and then re-distort it again, I get a little quality decrease. Is that normal?

Just asking, because when doing all the undistortion stuff, is it better to apply the distortion at the end of the comp to all CG elements and the merge it with the original plate?

I just thought I comp all the way down with the undistorted image + cg stufff and apply the Lens Distortion node at the end to the final comped image again. But this would decrease the plate quality slightly. or am I doing something wrong (look at screenshot)?

Thx a lot!