Using the Motion Sketch on the bird... (holding CTRL while moving mouse) You see the two points I am using to move the birds wings simply up then down. You can see that it leaves a residue of the birds wings as it flaps. I'm using very minimal movement. At first, low mesh.... and it was much more apparent. Now, my mesh is up to 1000 and this is my result. You only see it near the last wing motion flap, but still there. I also have a simple wiggle effect on the bird as well, not an expression. Is it just an anamolie... Will you see that in the render?
Expand the mesh a little bit.
I just jumped on here with the same qquestion/problem! "Expand the Mesh"... perfect.
I have a nested comp (a trombone players head, arm, hands and instrument) that are looping. I wanted to apply the puppet tool to his body to have that move a little as well, but not as complicated as the "head" comp. However, every time the nested comp moved outside the bounds of frame 1 (where the puppet tool had been applied) there were little artifact outlines of the initial frames shape. Hard to explain, but expanding the mesh to include the whole range of motion removed the artifacts.