This bug is a parity issue. When you try to fill the cauldron using water/lava drips from the dripstone, it doesn't fill the cauldron at all.

How to Reproduce
1. Create a water/lava source.
2. Place pointed dripstones (at least 3-4 blocks tall from top to bottom) underneath the block below the water/lava source.
3. Place a cauldron below the dripstone.
4. Either wait or speed up the random tick speed.

Observed Results
The cauldron doesn't get filled up.

Expected Results
The cauldron should be filled up with Water/Lava.