Ah-HA! Figured it out by reading Rayman's post, you have to toss your cookies, so to speak lol. In other words, clear out your browser's cookies and you should see new pic. I assume MLS is not programmed to replace your avatar cookie. Everyone else will see your new avatar except you until you clear out your browser's cookies. Hope that helps.
First I would try Tom's idea with refresh. If that does not work, hold down the shift key and try the refresh while the shift key is down. This at least used to cause the browser to totally replace any files for that page. If that does not work, then worry about cookies and other more intensive things.