I have a weird bug which occours when you want to create custom block models and destroy them in survival mode. This issue appears with every block which has cube-elements positioned outside of the 16x16x16 boundaries. It seems that the texture-atlas just uses parts of the texture which sits relatively next to the break animation.
I attached a screenshot to show the issue on a custom modeled fence-gate (open) which has its door hinges outside the normal dimensions.