I have a similar issue, though slightly different. Same, same, but different. I started building a new base on top of a post near the picnic table. For accessibility reasons, I built most of it out of grass planks, with the intent of upgrading as I go along. When I wanted to recycle one of the grass flooring pieces, it destroyed my entire base and everything inside it as a result. This does not make sense considering that I am destroying a floor piece in the middle. All other pieces are still supported by other flooring pieces. I tried straight-up just placing the blueprint over the grass piece and building it, but that also destroys the entire base. The flooring does not say that it is supporting anything. I've placed scaffolding and pillars as an attempt to counter the demolition, but that does not change anything. It still destroys the entire structure. Thinking about moving back to my starter base as this is proving to be more hassle than I had initially expected.