Need some help with copy rotation constraint

I am trying to make a tornado (80 x 80px - game)… I have lost a lot of nerves until I came with this rig. However at frame 20 (180 degrees rotation) mesh becomes squished.

Blend is at:

At frame 22 it cames back to normal until the end

Just a quick look I cant tell you whats happening but changing the position and/or rotation of the highest bone can overcome your problem.

Just an idea… hope it helps