When mining a cauldron filled with lava, the cauldron does not drop as an item.  It does drop when filled with water.

Steps to reproduce:

1. open a world in Survival mode, any difficulty.
2. Place an empty cauldron.
3. Fill cauldron with lava bucket.
4. Mine filled cauldron with pick axe (I used an iron one).

Observed Results:
Cauldron is destroyed

Expected Results:
An Empty Cauldron should drop as an item to be picked up by the player.  You lose the lava that it held, but retain the Cauldron.