It might be technically possible because the Walrus was fitted with two wooden 2-blade props one-in-front-of-the-other, so one of them could be fitted backwards. I'm a little surprised that this scenario wasn't prevented by having an unequal bolt spacing (so the holes only line up when the props are the same way around), and even more surprised that it wasn't spotted by either the installer, the inspector or the pilot on his walkaround inspection. But every now and then the holes in the cheese line up, especially in wartime.