Put the summary of the bug you're having here

What I expected to happen was...:

the splash potion of weakness would affect a zombie villager so I could cure him

What actually happened was...:

the potion warped through the ground and disappeared and did no effect to the zombie, tried multiple times on different blocks (dirt, cobble stone, wood, gravel,).

Steps to Reproduce:
1. make a splash potion

2. try and throw it.