This is caused by the webbrowser, it keeps the icon in cache and does not clear it very often.

Try it on another pc or another browser.

On the browsser with the issue, there are some lame tricks tha sometimes help get the browser to clear it's cache. Like ctrl-F5, or move the icon (if possible, depends on browser), remove favorate, press ctrl-F5 and create a new one....

see for more tricks: https://stackoverflow.com/questions/2208933/how-do-i-force-a-favicon-refresh

just try a few, or just wait, eventually it will take it over.