When mob standing on stairs, lingering potions will not affect them.
What I expected to happen was...:
The lingering potion must affect mobs on opaque blocks.
What actually happened was...:
Instant damage lingering potion, when thrown on the block near the oak stairs does not affect on the oak stairs on mobs.
Steps to Reproduce:
1. Place any block near any stairs block, then throw lingering potion on that block.
2. Throw lingering potion straight on the stairs block.