My pleasure, Ray!

When skins are processed they are treated like that.
Since the have stronger and weaker spots, they will stretch differently.
When they will be released before they are completely dry, the texture did not break and as soon as they are getting humid again, they remember and return to original shape. You can keep that at bay with a cutting in a clever direction (crossing the back line) but for a bigger number of strops most manufacturers probably won't. So you just have to nail them again.