This has happened to me before. When you upload an image from your computer to your avatar (not an offsite image), it just comes up as the one you had before, right? I found that if you fiddle around with it for a while (use different images, remove your avatar for a while, etc.) it usually resolves itself. If worst comes to worst, you could always just upload the image offsite (Brickshelf, Flickr, etc.).
And I have no idea how Doc can see your new avatar. I can only see your old one. What browser are you using? I've found that in Firefox (the one I'm using right now) I can only see your old avatar, but in Safari, I can see your new one.