This is an annoying bug. To reproduce it, load Google in Epiphany and then quickly press "Ctr+L" to re-focus the address bar. The page will steal focus from the address bar shortly thereafter.
Believe it or not this seems to be a regression from 2007. Before that time a widget would only grab focus if it was backed by a real widget. Nowadays it grabs focus no matter what. If there is no real widget, it forces the WebView to grab focus.
Here's the change in question: http://trac.webkit.org/changeset/24963
Another interesting data point is that we were very diligent in making sure this bug also existed in WebKit2.
Created attachment 125451 [details]
Comment on attachment 125451 [details]
Clearing flags on attachment: 125451
Committed r108278: <http://trac.webkit.org/changeset/108278>
All reviewed patches have been landed. Closing bug.