Overpacking can result in the same problem. This style of luggage is visually looking like they hold more stuff inside. It is comprised out of two parts and it closes with a clamshell method which is connecting the two sides in the middle. You could pack stuff on each side which is more convenient if you are an organized type. However, if you manage to pack more stuff inside, you will probably overpack the luggage which would make the zipper prone to cracking.