I am not positve if this matters, but I use Internet Explorer. I also have windows save my passwords and do not have my temp internet folder or history cleared when closing browser. (These options MAY have something to do with it.)

ok... so when composing a message and when I get to the URL image box, if I put my curser in the box and hit my curser arrow down, a "list" will appear of the images I have posted in the past. (Unless I toss all my cookies, clear my history folder manually or erase them)

BUT - I had to have POSTED the image - it won't show up if I just uploaded here.

It sounds complicated, but it isn't. It works the same way as when you log into yahoo or some site and you start typing and windows fills it the field for you.
Does that make sense?