Since the firsts snapshots water columns have been generating if there were at least two water blocks (Both source or flowing) on a vertical column. When the bubbles generate, the blocks of flowing water on top of the soul sand / magma block would become source, and if the bubbles stop, the source blocks would become flowing water again.
But in pre-5 the flowing water would remain source even if the soul sand / magma block is removed, and now in the pre-6, the bubble column won't generate if the column of water is strictly made out of source blocks.
What is the intended way to generate water bubbles? Is this a bug or the rules for creating the columns have not being determined yet?
Works as intended based on the fix of MC-130464