Cool steam vent creates more hydrogen from hydrogen.

My steam vent was behaving wierdly. I've pumped this area for hydrogen before. I could've sworn that I pumped much more than when I now checked. Pressure was about 4-6 kg/tile now.
I thought that maybe something reacted with hot temperatures and created hydrogen. Checked to see what happened with steam only, nothing. Checked what happened when I added hydrogen, I got more hydrogen.

Pay attention to my mouse pointer: I create 2000g of hydrogen at 00:30. Steam vent starts errupting and I check pressure per tile at about 02:30. Pressure equalizes at around 50g/tile.
Steam vent starts errupting and I check pressure again at about 05:40. The pressure is much greater after the second erruption.