It seems that even when building with "build-webkit --qt --debug" both, debug and release are being built for some objects. Linking the release objects then fails because of missing symbols.
Created attachment 118009 [details] patch for review.
Comment on attachment 118009 [details] patch for review. Clearing flags on attachment: 118009 Committed r102110: <http://trac.webkit.org/changeset/102110>
All reviewed patches have been landed. Closing bug.