Also using 4.2, in a Windows 7, tried to different computers both with Win 7 (Home & Work).

Here print screens:

- 3D view in the same WINDOW, grey, noting there in the 3Dview, image:
http://i.imgur.com/Xl0kVEh.jpg

- If I SPLIT the 3D View in another window, it works, image:
http://i.imgur.com/Iwv29uG.jpg

- I moved the chair in the left room, and draw two walls, the chair inst updated and the walls appear but oddly shapped, image:
http://i.imgur.com/C6IrVt2.jpg

Puybaret can u change any furniture around save the file and re-sended to me? lets see if this way it gets fixed for me.

THANKS! if u need some more information plz tell me.