Steps to reproduce this very minor bug:
1. Set your graphics to Fancy, in order to enable leaf transparency.
2. Go to the Swamp biome or create a similar environment.
3. Go to a tree with water on the background and start hitting leaves or and / or vines.
Then you can see that the water around the cracks no longer renders.
Related issues
Comments

I can confirm, but probably duplicate of/relates to MC-35920