In the Shadow of Two Gunmen: Part II - S2-E2
Other mistake: When Toby tells Sam to "Go back to the office", the subtitles add "Let's", suggesting both are going, but only Sam leaves.
Other mistake: In a scene with Leo and the President, Toby confronts them about the fact that there was no clear person in charge while the President was in hospital after being shot. He references the shooting as taking place 'last May'. However, in an earlier episode, 'The Midterms', there is a title card that states the date as August 14th and in the scene that follows there is discussion about the staff job approval in which CJ states, 'A week ago the job approval is at 51, we got shot at and its at 81.' This would mean that the shooting took place in August not May.
Chosen answer: A really annoying innate lack of sense. My friends and family say the same thing all the time, and I'm endlessly trying to correct them. I think people just don't know any better and (ironically) couldn't care less that they're speaking incorrectly.