From the snapshot notes:

1. Stalactites drip water (or lava if there is lava above the ceiling)
2. A stalactite with a water source above the ceiling will gradually fill a cauldron below with water
3. A stalactite with a lava source above the ceiling will fill a cauldron below with lava after a while

Current observation:

Stalactites drops water/lava bellow them if there is water/lava above their ceiling

But they only fill cauldron if the Stalactites is exactly 1 block high. If the stalactite is 2 blocks or bigger they drop lava/water but it won't fill cauldrons.

Tested with Lava and Water using full sources (non flowing).

Expected behavior:

drops coming from Stalactites should fill cauldron no matter their height.