OK I made a change so that it will fix the issue for everyone without needing to reload.
It happened due to a "caching" issue - we set images and other files on the site to "cache" for a long time, which means the browser doesn't keep downloading the same images every time a page is opened. With the form changes and stuff the image needed updating :)
Good news: the proper Kyurem sprites are shown on http://pokemondb.net/black-white-2/exclusive :D