Seems to be a legit bug, we are setting an identifier as the selected navigation item instead of a NavigationItem.
Created attachment 309546 [details] Patch
Comment on attachment 309546 [details] Patch r=me
Comment on attachment 309546 [details] Patch Clearing flags on attachment: 309546 Committed r216546: <http://trac.webkit.org/changeset/216546>
All reviewed patches have been landed. Closing bug.