water goes through slabs (at least oak ones)

 

What I expected to happen was...:
the water would stop after being stopped by the slap (this was vertically)

What actually happened was...:

the water continuced though the slab as if it were not there. the slab was in the top half.

Steps to Reproduce:

1. put water currounded 
2. ... place slab in top half postion
3. ...