bubble columns don't work in waterlogged blocks

The problem

When I try to create a water column with trapdoors in it the trapdoors doesn't seem to count as source blocks and doesn't transfer the bubble column upwards

Why it should be fixed

**this may very well be an intentional feature but I don't think it serves any purpose since I don't think it's powerful enough to be considered overpowered; It's just a nuisance.