The HTML spec changed in https://github.com/whatwg/html/pull/3970. See https://github.com/whatwg/html/issues/2555 for further background. A test is available at https://github.com/web-platform-tests/wpt/blob/master/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/url-fragment.window.js
<rdar://problem/44282736>
Created attachment 350971 [details] Patch
Comment on attachment 350971 [details] Patch Clearing flags on attachment: 350971 Committed r236560: <https://trac.webkit.org/changeset/236560>
All reviewed patches have been landed. Closing bug.