Slowness when running on grass pathways

I should be able to run at the normal running speed on grass pathway blocks when I use them with a half slab.

When I started to run onto the pathway from the half slab it slowed me down like if I was running through soul sand or if I was affected by a spiderweb.

Steps to Reproduce:
1. Make a grass pathway
2. Put a half slab on it
3. Make sure the half slab has a layer of blocks which are on the same level as the slabs
4. start running