Jumping up and down breaks blocks leaves break marks until you begin to break a different block.

How to reproduce

• Find a tree, preferably a tall one.
• Chop down all the logs hat you can reach.
• Jump up and down to break the next block above. You should not be able to reach it, more so, break it.
• By jumping up and down whilst holding left click, you should start to see the log breaking.
  The break marks stay there even after leaving it half-broken, until you begin breaking a different block.