Catalogers are a weird lot, I think

So I'm sitting here reading Chapter 4 of the Students Guide for LIS 703, and Helen Humeston, the professor and co-author of the guidebook knows how very dry the Anglo-American Cataloging Rules are, so she livens it up a bit in her own writing. Usually this means she just writes cleverly about boring things. But suddenly, I read the sentence:

"Now we come to the only faintly humorous part of AACR2. Rule 21.26A governs the way to enter a work dictated from beyond the grace. Princess Diana has been busy since she died. She is credited for two spirit books."

And then there's a bibliographic record where the MARC field looks like this:

600 00 |a Diana, |c Princess of Wales, |d 1961-1997 |c (Spirit)

And, sure enough, the actual cataloging rule says this, "Enter a communication presented as having been received from a spirit under the heading for a spirit. Make an added entry under the heading for the medium of other person recording the information."

The medium? Um, can I just say—WHAT were they thinking?!!?