This "bug" involves aggressive mobs willingly jumping of blocks when the player shifts at the edge of a block.

Image 1 shows the normal condition. When the high is 3 or more and the player is standing on blocks. In this case, the mob doesn't walk of the edge.

But if the player shifts to the edge,the mob instantly jumps of the edge (only seems to happen when the pilar is between 3 and 12).

Image 2 shows that if the player does the same on top of a trapdoor, since the entity sees it as a full block (correct me if I'm wrong), doesn't jump.

This might be because the bock the player is standing is the air block, if you check the F3, the block coordinates indicate that. 

I think  that the behavior in the Image 1 is undesired and strange, and the Image 2 is fine.