When it cuts to commercial, Bill Bixby is pointing the gun at Barnaby Jones with his left hand, and the P.O.V. is his, a hand close-up. When the camera cuts back, the P.O.V is Barnaby's and Bixby is holding the gun in his right hand. When he made The Magician, he'd said that if his character, Tony Blake, would need to hold a gun in a scene (such as Lightning on a Dry Day) he refused to hold it with his dominant hand, so he held it in the left. This was The Magician era, 1973.
The eyelids of Denise Fraser (played by Claudia Jennings) move while she is in the trunk of the Rolls Royce, supposedly dead.
You notice in the first scene that the front door opens one way and when Barnaby Jones appears at the house it opens another way. It also has curtains in the opening scene and then changes completely when Barnaby appears.