Based on checks in IE8, IE9 (Windows 7) and Opera 9.63 (Ubuntu Natty) it looks like thumbnails not generated through the FileAPI (bug 29248) may be currently broken in production on Wikimedia Commons.
In a nutshell, thumbnails for images in these tested and probably other browsers either appear as white boxes, or as the broken thumbnail image, on any step in the process. Clicking the image does result in an enlarged preview.
For reasons that are mysterious even to me, I've used
http://www.fishfarmingbusiness.com/wp-content/uploads/2011/03/FishDancing.jpg for testing purposes.