While I was working on a map that uses the bubble_column source blocks (BCB) as an element, I noticed that BCBs don't create bubble_column blocks if the water above is "flowing_water". Now for most of the different block types that flowing_water represents, this is perfect, but if it's level 8 (just like it is in a water_fall) you can't use this technic. This is maybe not a bug more of a feature I would like to see but I think it's something that needs correction.
Furthermore it would totally make sense since flowing_water with level 8 looks exactly like water.