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My best guess is that your mount wasn't correctly polar aligned. From Melbourne (so not too unlike many places in Australia), using an alt-az mount or without optical aid, Venus appeared near the bottom of the Sun on ingress, moved upwards and a little to the left as it crossed onto the face of the Sun, then slid off the Sun heading to the lower left - an apparent U-shape. But that's an illusion due to the changing orientation of the Sun during the day, combined with Venus' actual straight line across the Sun's face.
With a correctly-aligned equatorial mount, Venus' apparent path would have been straight across the Sun. With the mount incorrectly aligned, it is possible for you to create a variety of curved apparent paths for Venus across the Sun, depending on quite where the polar axis was pointed. A diagnostic test of poor mount alignment would be that you would have been having to adjust the declination axis all day as you tracked the Sun. If you didn't have to do that, I'm mystified!
Could there be any other source of image rotation, either of the camera (fixed on the eyepiece or separately mounted/held?), or in post-processing of images?
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