Slitherine

Note (a tale of) two Villages here. When you have Palisaded Village you can't upgrade the Fortified Village to Rudimentary Fort.

Current solution, tear down the Palisaded.
Don't know if there is a problem the other way around or there is no upgrade.

Possible solutions:
- Don't allow the Fortified Village to be build if Palisaded exists, but allow that to be upgraded to Rudi for cultures that has that.
- when upgrade to Rudi, just remove the other two.
- when a culture takes over that can't build it, just convert it to the one that that culture can.
- Just allow the upgrade and keep the village.

It's normal in the sense that most buildings (except some religious ones) are retained even when they can no longer be constructed, and that's largely for the better, among other things, it prevents a captured region from losing all its buildings at once.
So indeed, if a nation with a different building tree takes over, there will be some conflicts, and it's your responsibility to destroy the buildings you no longer want. This situation occurs in quite a few cases.
So I’d say it’s up to you to demolish the buildings you no longer need.