Absolute Zero?

[Morloc]

I'm doing one of the scenarios I really love to play. The planet has been torn out of orbit and is getting progressively colder. I throw in Cold Snaps which can stack 4-6 deep for added fun.

I was pleased to see that the temperature does cap out at -460F (absolute zero).
I've been having a blast with this run and have been playing for a long time since seeing the temperature first hit -460. I'd been having to keep up with more concentric walls and tons of heaters.
Everything was very stable, but lately I've been losing crops to the cold. It almost feels like the actual temperature outside is creeping lower that -460F even though the thermometer doesn't show it.

Would this be possible with the underlying temperature mechanic, or is the displayed -460F correct and something else is causing the issue.

1) Power to heaters is uninterrupted.
2) No architecture changes that'd make the greenhouses colder.
3) No stuck doors.
4) No missing roof tiles.

Could the Cold Snaps be driving the effective temp below -460F? Even so, nothing was out of the ordinary there. I had 5-ish Snaps stacked, which has been the case for years of the game.

Thanks in advance for any insight!

-Morloc