Recovered from the browser cache of: Sir Real
The author writes:
That's the only problem with having a buffer. By the time this comic came up to be published, I had realised it wasn't funny at all.
Also, since it looks like no one's ever going to notice the extra joke in No. 1278, I might as well explain it at this point. The musical score Margaret is holding displays a third-related modulation. Because she's disguised as Priscilla Emptor the Third. (Well, I thought it was funny.)