I don't understand Web Inspector messaging model, but upcoming patch makes Inspector work for me in practice.
Created attachment 165175 [details] proposed fix
<rdar://problem/12347373>
Comment on attachment 165175 [details] proposed fix Clearing flags on attachment: 165175 Committed r129250: <http://trac.webkit.org/changeset/129250>
All reviewed patches have been landed. Closing bug.