Skeletons move quickly at the Player, when targeting the Player and on bottom-half slabs.

What I expected to happen was:
Skeletons moving at a normal pace at the Player, when targeting the Player and on bottom-half slabs.

What actually happened was:
The Skeletons moved at a normal pace until targeting the player, which then they start "running". (They may have also started to shoot arrows faster than usual as well, but I am not sure.)

Steps to Reproduce:
1. For convenience load a super-flat world for demonstration in Minecraft 1.14.3 or 1.14.4 (Doesn't have to be a super-flat, it can be any world type).

2. Create a bottom-half slabs surface (I used stone brick slabs) anywhere.

3. Spawn Skeleton/s or lure some onto the slabs.

4. Make sure the Player is in the Survival gamemode.

5. Be within the vision and range of the skeleton/s, and have them target the Player.

6. The Skeletons now "run" quickly at the Player.