Why does the author's vendor number disappear into an uneditable non windown when the isbn number is entered and ENGLISH is chosen as the language of choice?

Upon going through the publish features of iBooks Author, the author's vendor number disappears and there is no 'window' in which to re-enter or edit that number. This happens after I entered the ISBN number and then chose ENGLISH as the language featured in the book. Two hours on the phone with an apple rep did NOT solve the problem. MORE hours on the phone loom. Smells like another bug. My book? A 315 iPad page book with nearly 500 images, approx 700 mb. I think no one at Apple actually expected anyone to produce a real book taking advantage of the digital media. I see "pamphlets" on the iBooks app, ie. 30-40 page pamphlets, NOT real books. Anyone have a clue? I don't.