Potion-filled Cauldrons can be filled up with the said potion when there is a pointed dripstone with water on top of it dripping the water directly to the cauldron.
How to reproduce:
1. Place a cauldron
2. Put at least one bottle of a potion (It can be splash, lingering, or bottled) in the cauldron
3. Place a dripstone 2 blocks above it with pointed dripstone pointing to the cauldron
4. Place water above the dripstone
Nothing happens, or the cauldron will play explosion animation and empties the cauldron.
The Cauldron is getting filled up with that potion.
This removes the point of brewing more potions or turning more potions to splash or lingering.