Mob heads don't break faster with a tool

Put the summary of the bug you're having here

What I expected to happen was...:
A mob head would break faster in survival mode if a pickaxe is used, as when placing them they have the same sound as stone. Stone sound also plays when a player walks on them.

What actually happened was...:
The mob head did not break faster with a pickaxe or any other tool. It's possible that this may be an intentional game design feature.

Steps to Reproduce:
1. Place down a mob head (Also works with a player head)
2. Attempt to mine it with any tool
3. See that it does not break faster. Enchantments if any are applied, also do nothing.