Creator Backlash: Beagle doesn't dislike the book. He's just puzzled as to why people love it, considering it one of his lesser works.
He's also very intimidated by its success and knows that he'll never get it quite that right again.
Development Hell: A live action film adaption has been in development since 2005. So far it's lacking funding, there's no finished script and the only confirmed cast member is Christopher Lee. Word is that the rights to the book are in the hands of a lesser director in Germany, and will once again be in possession of Beagle's company in 2015, at which time the chance of a movie happening may be bigger.
Word of God says the project was never really going anywhere to begin with, and Lee was never really on board, just talked with.
Promoted Fanboy: Christopher Lee was a huge fan of the book, to the point of bringing his own copy of the book to his recording and pointing out lines that he felt had to stay in the story.
Throw It In: The cat's pirate voice was ad-libbed by his voice actor who was having fun with all sorts of accents to give the cat, and everyone loved the stereotypical Long John Silver voice that they just had to go with it. They gave the cat an eyepatch and peg leg to match.
"Have a taco" came about when Beagle was writing very late at night, when you start writing all sorts of strange things. However, he loved the line so much he had to leave it in, Anachronism Stew be damned.