The bug only appears to happen if you get close to the 4 borders corners it affects the player and mobs to jump out of water.
(By Affect I mean these block acted as a full block when they aren't,)
Block that I tested that affected the player that usually walks over them was water once you enter it you couldn't jump back to land, with stairs you need to jump each step like it were a block, slabs, trap doors, soul sand, carpet,4 layers of snow, flower pot, turtle eggs, Lilly pad.
Also, Bed Haybail and Slime block that should make the player reduce fall damage didn't work.
Also if using spawn eggs near the border will make the spawn behind you, not in front.

Grassblock´s in these corners sound like stone.

The issue disappears when made into infinite.