Created attachment 142703 [details] screenshot When 'Show user agent styles' is enabled in Settings, this bug happens. I confirmed this bug on Web Inspector of WebKit r117557, Windows 7 Hthis bug happenome Premium SP1 64bit.
Created attachment 142708 [details] Patch
Committed r117587: <http://trac.webkit.org/changeset/117587>
I confirmed this bug fix on Web Inspector of WebKit r117603. Thanks, Alexander Pavlov, Yury Semikhatsky!