http://lists.gnu.org/archive/html/emacs-devel/2010-03/msg01124.html
+The exception is, if you know that the change will be difficult to
+merge to the trunk (eg because the trunk code has changed a lot).
+In that case, it's helpful if you can apply the change to both trunk
+and branch yourself (when committing the branch change, indicate
+in the commit log that it should not be merged to the trunk; see below).
+
* Backporting a bug-fix from the trunk to a branch (e.g. "emacs-23").
-Label the commit as a backport, e.g. by starting the commit message with
-"Backport:". This is helpful for the person merging the release branch
-to the trunk.
+Indicate in the commit log that there is no need to merge the commit
+to the trunk. Anything that matches `bzrmerge-skip-regexp' will do;
+eg start the commit message with "Backport:". This is helpful for the
+person merging the release branch to the trunk.
http://lists.gnu.org/archive/html/emacs-devel/2010-05/msg00262.html