Hmm indeed, I'll ask around and see what I can come up with.
I did notice on your portfolio that you did had a blurred preview image of the marmoset viewer when it's not active, however this doesn't seem to be the case for me: http://www.rafaeldejongh.com/pokeballs/ (at the bottom of the page).
So I assume this has to do something with the thumb image getting a 500 error?