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 paintings 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 removes the cup of coffee from the machine (which should have taken some time for the machine to fill). 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, where Columbo puts the cup on a table after having never once taken a sip of 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.
When Columbo sets down his coffee cup and unrolls the painting of the blue horse, he holds the painting open with both hands, left hand holding his cigar. Camera changes to a shot of the painting from Columbo's perspective, now held only with his right hand, left hand gone. When the scene reverts to the previous camera, both hands again hold the painting, but now his cigar has impossibly transferred to his right hand. Also, the coffee cup which Columbo set on the table has moved, now twice as far from the edge as where Columbo placed it.
At 25 mins. when Columbo questions the painter Sam, the model obviously doesn't look anything like the woman Sam's painting and even her pose is completely different. It wouldn't matter if she was there or not.
In "Prescription: Murder", the reception room of Dr. Fleming's office features a distinctive painting (trees and white houses with red roofs) which is shown in several scenes. The same painting appears in "Suitable for Framing", as part of the art collection sliced and stolen by Dale Kingston.
When Dale sits for makeup removal, his elbow collides against Columbo's cigar, end on, revealing that the cigar is unlit. When the camera changes from the two-shot to a wide shot, smoke reveals that the cigar is lit. It's also clear it left no mark on Dale's white stripped dress shirt.