If you load a website that has the Upgrade-Insecure-Request header, then navigate to a second site that does NOT have the header set, WebKit will continue to process resource loads as though the UIR header was active. While we want to perform sub-frame loads with an inherited UIR state, we do NOT want this to happen when performing a top-level navigation that replaces the content of the frame.
<rdar://problem/27075526>
Created attachment 286189 [details] Patch
Committed r204521: <http://trac.webkit.org/changeset/204521>