This isn't really a bug, the extra CO2 is coming from the PLNT, when it converts it into oxygen, it slowly creates more OXYG than the CO2 it used up (I think).

I did see a bug with the website though, the open button on that save is broken, it links to ptsave:949994#[BUG?]%20CONV when it should link to ptsave:949994#_BUG___CONV in order to work (the button after you hit view works like that)