I also fixed the problem by deleting the existing logo and then adding it back in. Looks like it might be creating new sizes of the logo to conform with @media types (just a theory, I haven’t looked at the code carefully beyond Firebug).
Also, I had created a style for the logo div in my child theme. The 1.7.x stylesheet notes that is now deprecated and the logo is displayed with an img tag instead, so check any custom style.css after upgrading.
Hope this helps.
