In the limousine as David Buckner is opening the cigar box, he removes the piece of tape on the left side. As he removes the piece on the right side, the piece that was on the left side reappears.
In the cable car near the end, the black tape strips on the box disappear and reappear without anyone removing or reapplying them.
The position and amount of the plastic string in Columbo's hair changes from shot to shot.
In the elevator scene as well as in the scene that follows where Columbo is standing on the small and narrow road in the mountains, the character obviously suffers from vertigo; however, a few scenes later he is walking down the high metal staircases at the outside of a factory building and suddenly his vertigo seems to have completely disappeared.
Near the end, the door on the cable car switches from opened to closed between shots and reverse shots.
The deaths occurred in Palm Springs, CA. This is in Riverside County and is nowhere near Columbo's jurisdiction. Just because he was told to look into the possible disappearance by a supervisor, once the deaths were established to have occurred outside of LA County and the city of LA, Columbo would not be involved in any investigation.
When Roger is looking in the rear view mirror at D.L.'s departing limo the image is a straightforward view of the departing vehicle instead of the reversed image that would actually appear, revealing it to be an obvious crop of the film image into the outline of the rear view mirror.
When Roger is sitting in his car and lights his cigar, you can tell that it had already been lit and put out.