I have searched the forums and not found a solution; so this is a "responsible" post.
I have installed two separate wp1.5's in two separate databases. In both cases I replaced kubrickheader.jpg (in default/images) with a different, personalized picture of the same name.
One on blog, my new picture shows up. On the other one, the old blue bar is still there. I cannot see that I have done anything differently.