Please have a look at this screenshot:
http://www.richardvankooten.nl/webspace/missing_smiley.png

As you can see there's just one smiley image that is constantly missing. I tried replacing the image with another image, tried deleting and manually re-adding, tried installing the dev-version, nothing worked.

Then I noticed in Firebug that this one smiley as a weird, garbled css-class assigned to it. Has someone here come across something similar? Suggestions on where to look for a solution?