It basically just "flips" where the seem is from the left side to the right side (basically the difference between like American comics and Japanese manga). It's nothing terrible, just weird. If I had to hazard a guess, I'd say that it's probably caused by the fact that it's going down the pages and placing them left-right, bottom-up. I'm just spit-balling, though. I might take a moment to look under the hood to see what the code is doing later.