As I build new areas, the areas that are already built begin to lose 1/4 tiles. If you continue to build, they come back and others disappear. Eventually, they are permanent and you can do anything except lose all the design work and rebuild everything. I tried to make a quick template of the rooms to use again, but templates dont save any more. No matter if you select an area with missing tiles or not.
I submitted a bug report on it.