I still had to manually fix this for my shop. One model of mine has 5 images: the shapeways render, my render, and three photos. They are all of the "sandstone" material. I wanted the first photo to be the one that is used for the shop page, but instead, the shop page was always showing my first render (the 2nd listed image). Changing the material on my first rendered image from "Sandstone" to "Select a Material" was the only way that I could get the 3rd image (my first photo) to be the one chosen for my shop page. So, apparently, this is still not fixed.
hmmmm the title is shop image, but seems to deal with problems with images for one product. Nevertheless. I've tried to change my shop banner. And it seems to work. It's changed in the shop settings form. If I view the shop from this page it's also changed. But when I do a reload of the page or open the shop in an anonymous browser window the shop banner still remains the old one. (and yes I have cleared my cache and the old picture is also visible on my mobile) It seems that one update during the last week was successful but every change during the last days was not. Woody54