Hi. I am not sure if this is a bug or a setting. Status Quo: When walls intersect, their (out)lines merge. Also, one can copy / paste doors and windows from one wall to another. The cill / threshold lines dissappear / change colour automatically. The problem: In one of my models, suddenly some walls do not intersect/merge. Also, some walls are very stubborn and do not accept any doors / windows which have been copy/pasted on them. It appears they only accept doors/windows from the "design tools" tabs. In some instances, the copy/pasting is marginally successful: the door appears on the wall, but there are still lines drawn through both sides of it (normally, these lines are automatically trimmed). I am seriously stuck, and do not want to waste any more time. If anybody can help, I would be very grateful. Kind regards, Dimitar V Dobrev, Architect