I'm experiencing a weird and frustrating problem when trying to build my second house.

First of all, as soon as I get as far as the main hall on my second house, the three wings on my first house disappear... More specifically, they become walls again. My children still enter and exit these walls, but I can't. Secondly, when I try to lay up blueprints for the first wing in my second house, the blueprints disappear right back into the menu after about half a second, and do not show up at the carpenter's workbench. This basically means I can't build a second house... Anyone knows how to fix this? I can't seem to find any information about it.