Remember seeing something about this bug in a previous version's thread, but I've encountered it again and also found a workaround that may explain why it's happening? (Not a programmer)
Was terraforming in a brand new game, 1. 8. 0 and the environment tab of the colony refused to save my 0. 2 atm max for oxygen. Tried different formats, at one point putting in 00. 20 just to test if you know, maybe something weird would work, found that no matter what I did, if I put in a number in that max atm field, then immediately closed the colony screen it wouldn't save. However, if I switched over to another colony and back before closing the screen, the field saved properly. I didn't think to test switching tabs within the same colony, but hopefully this helps figure out what's going on.