I'm new here, so I don't know if this has already been brought up.
Neil Gaiman apparently has written a detective short story with a dead Humpty in 1984. It can be found here:
Coincidence? Or maybe Fforde unintentionally using something that he read years earlier and that had stayed in his mind? In the special features section for BOE it says the original novel had been written in 1993.
The lighthouse scene in WOLP created a similar deja vu with me, but it's more obscure, so I might write about that later.