Slitherine

In my SP game I occasionally get a message that the populace in a region has used an old abandoned palace for stones. This prompts the following questions;
- What is the cause for this?
- Is it a problem?
- Can it be prevented?

Thanks for any help.

Maybe your capital moved, and it's the old useless administration center?

its basically good, the abandoned palace is disbanded and you get a bit of infrastructure.

I don't think you have any control, I've seen it the turn after taking a region and then 30-50 turns later (or never).

Good? well that building was generating some decadence. Bad? it was generating some legacy.

You don't have control over it.
The abandoned palace is the former capital of a conquered nation. It's possible to have several in a single province.
You lose a building providing both legacy and decadence and get some infrastructure instead.

That's the way to trim their number down or otherwise too many would accumulate over time.