The Bug:

Mobs that are immune to fall damage, do not take damage from falling on to dripstones.

Steps to Reproduce:

• Spawn an ocelot above a stalagmite.
  →  Notice how when it lands on top of it, the ocelot remains unharmed and does not take any damage.

Additional Information:

I believe this affects all mobs that are immune to fall damage such as iron golems, etc...