When Dale Kingston is on TV lecturing about Goya, Kingston compliments him by saying he was the "penultimate artist." The word "penultimate" means "next to the last" so the word makes no sense in the script.
Dale removes several paintings from the wall. Then, when Tracy enters, we see her admire the paintings still on the wall, including two of the painting that Dale had taken down already. These two paintings not only have jumped back onto the wall, they also mended themselves where Dale had sliced them with a knife.
When Tracy leaves the mansion, she pushes open the sliding door that had been altered to look like it was jimmied open, and left it wide open while she exited the premises. Moments later, the security guard explores that direction and the sliding doors are once again closed.
While in the TV studio, Columbo asks Dale if the coffee machine works and Dale confirms it does. After Columbo puts coins in the coffee machine he instantly takes removes the cup of coffee from the machine (it would have taken some time for the machine to fill the cup). Columbo waves the hand holding the coffee around as if the cup was empty while talking to Dale. In the same scene we see the cup in his right hand, then it mysteriously disappears, only to re-appear at the end of the scene. At the end of the scene, Columbo puts the cup on a table after have never once taken a sip of the coffee.
Whilst in the TV studio, after having his make-up removed, Kingston buttons up the collar of his shirt and adjusts his tie. A few seconds later he again buttons up his shirt collar and arranges his tie.