If you put lava in a cauldron, the sound is incorrect because it sounds like water being put in a bucket.

How to reproduce:

1. Get a cauldron, water bucket, and a lava bucket.
2.  Go in survival mode if you weren't. If you are not in survival mode, type in /gamemode survival.
3. Place the cauldron down.
4. Get the lava bucket and put the lava in the cauldron by right-clicking on it.
5. Take out the lava from the cauldron. 
6. Now get the water bucket and place it anywhere.

It should sound like the lava being placed in the cauldron. If you place the lava in the bucket anywhere other than a cauldron, it sounds different.