I have built a two way bubble column using pistons and slime to swap the bottom block between magma and soul sand.

I find when I swap magma to soulsand, I'll get so far up the column, then it will be as if there is a roof. I presume the water sources above are still pushing down because the magma was there previously and hasn't updated yet.

When I swap soul sand to magma, I'm sent to the top of the elevator (Unless I'm already on the bottom floor) where I have to wait for the water sources to update their state before the magma pulls me down.

Not sure if this is intended design or not and I cannot confirm is this was an issue in previous versions as I've only just built it.

I've attached an example of the magma/soulsand swapper I have at the bottom.