This has me completely stumped. Books are coming out of my perfect binder with a spine that seems twisted. The covers are slightly puckered and won't lie flat against the book. If I slice one of the books into section on the guillotine, I can see that the spine is tighter against the book block in the middle of the book than on either end (ie there is a thicker glue layer on the ends than in the middle), which I guess leads to there being more paper in the middle of the covers than on the head or foot of the book, leading to this buckling. At first I though that this must mean that the cover clamp is bent or bowed in such a way that it is pushing the center of the cover against the book block a tiny bit further in the middle than on either end. But, when I lay a square on it, it is dead flat, as are the two squeezing edges of the clamp. I just can't figure out what is causing this.