I think I know why it does not flood. When the door docks are opened according to the game the water elavator is.
--A Sealable compartment/object
--That is currently open (door dock open)
--Inside a dry compartment
Therefore it does not flood. The door docks are working and it is linked to the outside but because the water elavtor is inside a dry room it does not flood.It is also connected to the elevaor shaft because it is inside it and has a open door,when I flooded the shaft the water poured into the water elavtor/where you stand.
Image 1 [i.imgur.com]
Image 2 [i.imgur.com]

The game uses center of mass to calculate where a physics object is because it already need's it to calculate physics and is usualy a good indication of the center.
In this image.
Image 3 [i.imgur.com]
The center of mass of the green tube/physics object is within the dry room because of all the weight blocks.The game does not relise the green tube is stiking outside into the water. Even when doors on both ends are opened it does not flood because it thinks that the tube and therfore the open doors are inside the dry room even tough one of them is opening to the ocean.