Lulu's global network of printers produce books based on the best fit for the job in a given region of the world. Some of the factors that determine where your book will print are; book size, binding type, order quantity, page count, delivery destination, etc. Based on those factors, your book could end up with additional blank pages at the back of your book depending on where the order is fulfilled. It is not a mistake or a defect in workmanship or process, it is simply an aspect of a highly automated global book production network. Minimize the potential for blanks by keeping your page count divisible by 4, and do not add additional blank pages yourself.