Problem with titan master figures

Has anyone noticed stress marks on their titan master figures/headmaster pilots. I just added Titans Return Skytread to my army of titan master figures. I was inspecting Titans Return Overkill and his pilot arms have gotten stress marks after popping off of the figure a few times.
Are stress marks common on dark colored plastic in this line or which ones are most know for stress marks forming near the ball sockets on the arms. ? Skytread/Flywheels on the other hand is fine.
Are stress marks common on dark colored plastic in this line or which ones are most know for stress marks forming near the ball sockets on the arms. ? Skytread/Flywheels on the other hand is fine.