The curve doesn't need to be as sharp as the Leica template makes out. It can be more sloping. I have had happen what you describe and it's a result of hitching in your cut as your go around the bend. Non-Leica (i.e., bottom loader Leicas) users won't understand since their film never has to do what the long-leader Leica film does, which is feed past the film gate into a closed sprocket channel. That never happens with any other camera. Anyway, a slight hitch in your cut can make the film split at that point and peel into the shutter curtain (had it happen - I've loaded probably a thousand rolls into Leica III cameras by this point - everything has happened). But, like I said, you don't need such a sharp curve. You really only need to cut off a bit more than the row of sprocket holes.