When Lottie and Ivy were speaking at the front door of Mona's house, the backgrounds in their close-ups were obviously just plain backdrops and did not match the pattern on the walls of the entranceway to the door.
Near the end of the final scene, when Sean McClory is saying goodbye to Perry Mason and Paul Drake, he accidentally says, "Goodbye, Ray" (referring to actor Raymond Burr). Then he catches himself and quickly says, "Goodbye."