Oil and Water Don't Mix...Oh, Wait It's ONI

Due to the order in which the Sim updates tiles, liquids and gases can exchange places around descending corners:

Consider changing the liquid lock to come from the bottom to avoid this behavior.

I think it's steam condensing inside the door as the door closes. The steam teleports in the first free tile going up as it turns into water. The same way airflow tiles teleport gas while it condenses to its liquid form inside an airflow tile. Builds using that "mechanics" of airflow tiles are more common than the ones that use doors to have the same effect.

3 hours ago, Peter Han said:

Due to the order in which the Sim updates tiles, liquids and gases can exchange places around descending corners:

Consider changing the liquid lock to come from the bottom to avoid this behavior.

Thanks for the link.  That explains the water teleport, I guess.  If it's supposed to exchange location with a gas, what happened to the steam it swapped with?  It should have condensed into water, however small the quantity.  I avoid most exploits so these physics engine "features" are definitely not on my radar.

As for the steam escape, sakura_sk seems to be on the right track.  I still think the door is bugging when a third element is present, water in this case.  As the door closes, trapped steam would get pushed into a matching adjacent element tile.  And water shouldn't be teleporting four tiles away, but get deleted just as if constructing a tile over a singular enclosed gas/liquid tile.

It's been quite some time since taming a cool steam vent, and I initially made an ascending lock when vacuuming.  With the blob inside the geyser, the phase change would push the crude to the floor and open an escape path.  I was pushing to get oil and plastic at this point, so due to the space restraints I didn't add tiles to constrain the crude.