That was done because we noticed on the last problem set that they were copying the problems wrong from the book; they were getting the right answer for what they wrote down, but they miscopied.
Did you, by any chance damage any of the discs or miscopy the information?
Even when it is supposed the text as published is somehow corrupt or miscopied, it is still taken for granted that the definitive version of the text as intended is a meaningful concept.
They also make mistakes-lots of them: they miscopy, leave critical items out, and conflate materials, even their own previous publications.