weird liquid flow effect in a room filled with sour gas

In the oil biome of my map I've seen some weird flow effects.

I first think there was 2 types of liquids, but the material alverlay show it's not the case.

It's not only located on the geyser, but every where in this room filled with sour gas.

I don't see this effect elsewhere.

I've make a small test with sandbox mode.

A small room with a layer of 190 kg/tile of petroleum and sour gas above :

The flow effect is more and more important while i fill the room with more and more gas pressure.

It's started to be clearly visible whith 1000 kg/tile of sour gas.

Also works with chlorine (and maybe other gas) and brine (and so other liquids)

Metis.sav