When I'm logged in and viewing my own items, the item image does not update when I click on thumbnails. However, clicking on the main image (which is always the default item image) goes to the correct zoomed large image, which then turns back to the default image when I click on it. The behavior is correct when I'm logged out, and the wrong behavior described above happens reliably when I'm logged in. It occurs in both Firefox and Chrome. Hope this helps to find and squash the bug.