The bug
No matter the effort, it is not possible to create a line or field of bubble colums. At best, a checkered pattern can be achieved, with the "faulty" slots only creating columns of 2 blocks height
(which also seems to be the maximum height any bubble column can be if it's an isolated "tower" of water with no water next to it)
This is a direct result of the fix to MC-125400, so it may be invalid.