Major Atmos got fucked up by building in space.

[Tribaja]

It's wierd that BYOND just kind of naturally evolved its own False Vacuum Decay but also terrifying.
Not sure I'd categorise this as Major since the workaround is simple (don't build rooms over airbridges).

See, that's what I thought too, but if you read it again you'll note that there was no airbridge (the kind you can activate) involved in the second instance which means it isn't connected to that. So that would imply that it happens even with just simply building in space or maybe even repressurizing which is pretty major.
I like the false vacuum decay theory though, would be some Dwarf Fortress-tier emergent bugginess.