Despite my affection for the episode, I admit that is a problem in that Columbo just assumes that Grace would automatically resume watching after fixing the film. Of course that I think is at heart perhaps the one great flaw of Columbo's methodology in that he so often assumes all people react a certain way and that isn't how it is with all individuals.
The bigger problem with "Forgotten Lady" is why didn't Raymond arrive earlier at the time when he should have assumed the film would be over?
I'm not sure if I'd characterize a lot of this as bad logic. I think it's more his methodology. He often says "gee that's funny", "or things don't add up." Often he's not going after airtight clues with perfect logic. Rather he's stacking up a bunch of clues that when added up point to the suspect. One example is in Death Lends a Hand when he's in the suspect's office and says that the suspect being left handed (he was ambidextrous)is a coincidence since they were just talking about a left handed murderer, and then the punchline, he says this case is just full of coincidences. He already had him pegged anyway as soon as he felt the ring on his left hand with the palm reading ruse. Again that by itself wouldn't prove anything but it leads Columbo in the right direction and to the final setup to trap the murdererer with the final piece of evidence that nails him.