Has anyone noticed that the portrait of "Mrs. Mellville" from Murder By The Book (Jack Cassidy may be my favorite recurring villain) is hanging from the wall in the club-house in The Bye-Bye Sky-High IQ Murder Case? I believe it is seen very near the beginning of the episode, kind of a long-distance camera shot, but it is most definitely the same painting.
I have mentioned this before, but Mrs Melville's portrait appears in an episode of "The Rockford
Files" called "Crack Back", but there she is
Mrs Harriet Bergstrom. Why not save a few bucks
on the props?...in the days before VCR's, who
would notice such things?
There is an interesting page on this topic in the Scrapbook section of this site...it is under the heading "Columbo Flashback". You should take a look at it. It lists a bunch of props and sets that were reused in different episodes.