Summary:
Swimming on mud blocks fills the player's screen with the texture of the mud block (as if the player is inside the block)

Steps to reproduce:

1. Place mud blocks underwater.
2. Swim over the mud blocks.

Observed results:
The texture of the mud block is displayed on the entire screen of the player (as if the player is inside the block).

Expected results:
Since the player is not inside the block, the texture of the mud block will not be displayed in entire screen.

Image: