I have this same issue... seems to me that occasionally Earthlink disconnects me, and a few seconds later when my router re-establishes the connection I often get the wrong IP. If I disconnect/reconnect, 99% of the time I get my static IP back.
I login with my email address. You say that I should login with my account MS #. What the heck is that? How do I find out what that is? I would like to try it out.