My money is on "genuine", for exactly that reason.
With focal-plane shutter moving from top-to-bottom on the camera, the lower edge of the image is always taken a few centi-seconds before the upper part, which is why props "of that era" often appear to be bent.
On the S&L photo, the lower blade is captured at an acute angle in its (RH) rotation, so appears short and has a high rate of movement relative to the camera, so is more blurred. By the time the upper part of the image is captured, the prop has moved on, the upper blade is more perpendicular to the camera, and has a lower rate of movement so is less blurred.
In the original, "climbing", image, my guess is that it is shown rotated by 90 deg anti-clockwise, so "up" is actually to the left of the frame as displayed. (Imagine how you would be holding the camera to capture the image from the student-seat of the training aircraft or station-hack that the subject is formating on). Hence, the apparently-right side of the image is taken earlier than the left, which accounts for the apparent bending. As the camera is now front-and-right of the subject, and due to the pitch of the blades, the right-hand blade is also relatively flat to the camera so is clearly seen whilst, by contrast, the left blade is leading-edge on, so is less clear.