Boiled down to their essence, I would think there must be a few episodes of 'Columbo' that have similarities with episodes of other murder mysteries.
I would think the basic outline of "Prescription Murder" must have been seen in plenty of them, for example.
Not that I have any solid evidence to back this up, but the one episode which always felt like it would have been at home as a Quinn Martin Production - like on 'Cannon' or 'Barnaby Jones', or as a 'Mannix' episode, would be "Swan Song". Jumping out of a small plane to leave the others to die just had that mid-70s feel to it for me.....
Luckily it's the details - and of course Falk's portrayal - that end up setting 'Columbo' apart from the rest of the pack.
Some here has posted -- sorry I forget who, but he'll probably jump in soon -- that the exact plot of "Columbo: Uneasy Lies The Crown", right down to details and dialog, was also done on another detective show -- I believe it was "McMillan and Wife".
Unlike Toby's discovery, I assume the casts were completely different.
I recall reading somewhere that Warners Bros used the same pool of writers for all the Westerns and PI series they produced in the late 50's and early 60's (Cheyenne, Sugar Foot, 77 Sunset Strip, etc). Often scripts for one were modified for the other. Is it possible this is the answer for some similarity?