What I expected to happen was...:

That mobs, such as creepers take damage from jumping on the stalagmites, or most specifically their top/peaks.

What actually happened was...:
The mobs avoid any of the damage that the player can get, even though they jumped the same way on top of the pointed dripstone; only take damage while falling from a high place directly on them.

Steps to Reproduce:
1. Take any terrestrial mob spawn egg
2. Spawn the mob on the stalagmites(rows of them with walls on sides)
3. Look for when it tries to jump to get around