What happens is that in order for your web browser to work faster and more efficiently it saves a copy of some internet files onto your hard drive (in cache) so that it doesn't have to keep loading the same picture over and over again.
Once you've changed your icon your computer doesn't know alot of the times, because when you upload an icon onto the server it saves it under the same name as your previous icon (which I'm pretty sure it's your nickname) and on top of that, your browser doesn't know because your new icon is relatively the same file size (under 2,000 bytes). So it keeps showing the icon in your cache For you.
Answer: Hit Refresh. It should fix it.
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