Gallery animation spins squashed image, not just circular spinner

What happens

When I go between images in the gallery, the circular spinner spings along with a squashed version of the image until the next image appears. (This does not happen when loading a non-gallery image, such as the featured image at the top of the linked post.

What I expect to happen

Having just the spinner spin, not the spinner and the squashed image.

The page I need help with: [log in to see the link]