As brought up by Ryosuke Niwa on IRC, Qt's Input Method API shouldn't be accessing the selection through RenderTextControl. We should go directly through the Frame's SelectionController instead.
Created attachment 72417 [details] Proposed patch
Comment on attachment 72417 [details] Proposed patch Clearing flags on attachment: 72417 Committed r70982: <http://trac.webkit.org/changeset/70982>
All reviewed patches have been landed. Closing bug.