Element being transfered through tiles

Sour gas is being transferred from the Crude Oil boiling chamber below to the Volcano chamber above it through tiles it should not be able to pass through.

The second picture shows the Volcano chamber as it's intended to be, sitting in vacuum. The first shows Sour Gas suddenly appeared up there. I must mention the oil is being turned into Petroleum in a very weird way. Instead of converting a whole cell of Crude Oil to Petroleum once it reaches the appropriate temperature, the game is creating new 5kg pockets of Petroleum, putting it where the ~840kg of Crude Oil once was and pushing the rest of the oil to the side. I was told this is called the "flaking" effect. This effect might be a different bug altogether. My main problem here is Sour Gas suddenly appearing where theoretically it should have no way of getting to.

Disclaimer: English isn't my first language and also my writing is bad in general, so if you need anything clarified, just ask.