Water flows doesn't form a source while on top of bubble columns

When the water flows connect on top of bubble columns, they don't form a water source block like they do on every other situation.

Steps to reproduce:

1 - Place a water source on a bubble column.

2 - Place another water source two blocks away.

Expected result: the flows connect and form another source in between.

What actually happens: the flows don't form a water source.