Love this software, which I just started using. Obviously I am new to it, but suddenly: 1) The walls from Level 0 are visible (in black not grey) in every level; 2) When I create a new level they appear as if by magic overlaid on the grey walls from the lower lever; 3) I am unable to edit or delete them. No doubt I'm doing something embarrassingly silly, but would appreciate guidance so I don't have to rebuild the 4 floor building from scratch again.