This has tripped me up numerous times. I've uploaded a picture to photobucket, forgot to resize it first, posted it, then gone back to resize it, and even after refreshing the picture in the post is still too big. What I have to do is navigate to a different page, clear my temporary files, then navigate back to the post, and it's sized correctly. I think that the reason is that the files for the images on the current page aren't deleted and so you have to go to a different page first. In any case, after resizing, you're the only one who still sees the picture full-size; it will appear 640x480 to the next person to view that page.