@Nescio this commit is probably totally unrelated, but in the replay uploaded at https://code.wildfiregames.com/rP22006#37234 we got a report from faction02:

After nani resigned, I also noticed that when clicking on his gaia skirms, we could see three buildings to build: military colony, Library and a third one that I don't remember.

(It says "palisades" in the chatlog from that match)

Does that possibly ring a bell?

Sorry, I don't understand what you mean, or what I'm supposed to say. Could you rephrase your question?
This patch improved the classes consistency of unit templates; structures are unchanged.
The colony and library templates were last touched by D1759/rP22256, but that was four months ago.

I was mostly wondering whether you remember an a24 template patch that changed the build list entries. But I tested on alpha 23 and the issue occurs there too. So I've reported it more properly at #5581.

Interesting. It seems those structures listed aren't random, though: they're just the ones defined in the specific templates (see e.g. rome_infantry_javelinist_b.xml), without the ones they inherit from their parents (esp. template_unit_infantry.xml). Perhaps it's a problem with the observer GUI or something?

Or perhaps an even simpler explanation: gaia_house doesn't exist, brit_crannog does. And palisades are gaia structures shared by all civs, so they show up too.