When building for example a town square and you move the camp flag (the blue start flag) it will put that flag in building schematics, so, it will never finish the building as you cant acquire more of these flags (to my knowledge).
So might be handy to exclude them from building schematics or anything like that.
If required i can add some screenshots, but i think it’s pretty straight forward.
It’s not that complicated, it’s the “flag” you plant to start the game. you cant create them, nor find more of them, they shouldn’t be put into building schematics and/or show up there.