I don't know what is the exact reason, either the pulling animation ends too late or the game changes the piston data too early however the result is that the animation of the retracting piston head causes z-fighting with the piston.
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Fixed in either 15w38a or 15w38b. Not confirmed for 15w44b.

Can anybody else confirm the fix?

Sorry, I was only looking at the normal piston. Please change title to sticky pistons then.

Confirmed for sticky pistons. They seem to have changed a little bit. Attached screenshot.

Left is sticky, right is normal.