diff -r 92a61d7618ac -r ce9696193175 mercurial/commands.py
--- a/mercurial/commands.py	Wed Feb 03 11:01:11 2016 -0200
+++ b/mercurial/commands.py	Wed Feb 03 08:59:46 2016 -0800
@@ -1682,9 +1682,6 @@
         if not allowunstable and old.children():
             raise error.Abort(_('cannot amend changeset with children'))
 
-        newextra = extra.copy()
-        newextra['branch'] = branch
-        extra = newextra
         # commitfunc is used only for temporary amend commit by cmdutil.amend
         def commitfunc(ui, repo, message, match, opts):
             return repo.commit(message,