If you break a magma block under a column of water the water will not flow down, if you remove it with a piston it will. I tried this in survival and creative.
Swapping Magma blocks and soul sand keeps old bubble direction
Pushing magma in place of soul sand or vice versa beneath existing bubble columns does not update the bubble column direction
Water created by a soul sand/magma block's bubble column does not update after removing the block
Bubble columns are not created when pouring water over magma block
Bubble columns don't update when placing magma blocks or soul sand above them