From the credits at the front of the book:
Design: It is impossible to list all of the creators of the items catalogued in these volumes, but credit goes to everyone who has created a magic item in a module, boxed set, accessory, hardbound, or magazine article published in the last 20 years.
User Information RE History of the Product:
TSR decided that the magic items avaiable for D&D would be collected in a leatherette-bound series of four tomes called the Encyclopedia Magica. While proofing the volume spanning A–D, a design director noted that, contrary to TSR's house style, the word wizard had been replaced by the word mage. So the director directed a lowly editor to change it all over. Which the editor did, but he neglected to specify a space before or after the search string "mage." So, for 16 straight pages, the book was filled with side-splitting passages like
"The user may look into the ball, concentrate on any place or object, and cause the iwizard of the place or object to appear. A crystal ball may be used three times per day, for up to one turn per use. The more familiar the object or area, the clearer the iwizard."
"The tower can absorb 200 points of dawizard before collapsing. Dawizard sustained is cumulative, and the fortress cannot be repaired (although a wish restores 10 points of dawizard sustained).
On and on, the scourge known as "Dawizard" destroyed magic items across the land.
After this incident in 1994 young editors at TSR, Wizards of the Coast, and elsewhere were inculcated with this tale by their stern-faced creative directors. "Dawizard" became the evil bedtime story that would keep these editors up at night, slaving away over a hot computer screen, fearing they would share that editor's fate if they ever failed to manually proof a book again. As it should be.
This story is told by Mike Selinker in 2009 in a livejournal post found here: http://selinker.livejournal.com/32929.html