your browsers image cache will automatically refresh every so often
making your image a different size will make your browser's cache redownload the image since it's a different size
the issue is now all avatars are stored under the same url unlike before
........ what about the same url?
Also, cache headers relate to file size (not image size - a different but identically sized omage will be a different size) not image size
I guess it doesn't hurt to try ctrl+f5 though, lord knows we don't need a 24th topic about this crap