Any mob will go running in circles over its own axis when stepping in half slabs. For this to happen, half slab must be on the upper half side. Downside half slabs wont have this kind of reaction. Another note: Even if you make a full block (Two half slabs) mobs will react the same way because they are stepping in the upper half slab.

I cant post an image because this bug cant be captured in an image so I have posted this video.
https://youtu.be/J4NFjs5lcuw