I found the answer in the user's guide. You have to right click and "add to home". I was just dragging and dropping which worked fine in one level. Should have read the guide before I started I suppose, but the app is so intuitive that I didn't think I would need to. Love it!

<t>Having placed furniture in level 0, I placed two items in level 1 successfully. After that when I try to add more furniture into level 1 it is rejected and the display jumps back to level 0. I have tried all sorts of remedies like closing the program and reopening, and completely rebuilding from ...