As discussed in webkit-dev it seems that a change in the svn commit hooks made commits in GTK+ stable branches to be shown in the buildbot and triggering builds that don't affect trunk at all. We probably need changes in the hooks but also in the buildbot config. See for example:
I believe that Lucas fixed this yesterday.
We now once again use the correct function to parse branch from path in the hook. This function raises an exception when the change is on tag or a release, so no buildbot config changes were needed.