When the Restoration Team had found out that the main entrance's sidelights were functional, they turned next to the identical sidelights found flanking the doorway between the Entry and the Drawing Room.  However, when the team searched the wall below the sidelights they could find no evidence of a space for the sidelights to pocket into.  Also, the sashes could not have pocketed into the wall above them because of the doorway's large fanlight.  The team was stumped until they removed an electrical box and looked at the wall framing beside the window.  What they saw was that a slotted rail had been placed between the window and the closest stud.