Mongoose will replace those books. I'd conact them about it if I were you.
They for a while tried printing their own books, and two common problems were warped covers and what you describe. They since have returned to using an outside printer.
Color hardcovers are from before and after the in house printing, as are all softcovers I believe. B&W hardcovers could be in house.
So you don't have to buy PDF. Some 'bad books are still in distribution channels, but if you get one they will replace it. Any books released since around a year ago and new titles should not be a problem.