I've been bulk rolling for a while now, and occasionally I'll get a few photos that look like this. To me it looks like something was rolled improperly with the sprocket holes slipping up a bit and then somehow the whole thing gets exposed to light just a tiny bit. Am I rolling it wrong? Is it a problem with the bulk roller? A problem with the film in the can before I even open it? Did I somehow expose the can to light? Did this happen while actually taking the photo? Any other ideas?