diff -r 46308fadaa15 -r 17011b36aac7 mercurial/context.py
--- a/mercurial/context.py	Fri Aug 15 02:39:01 2014 +0200
+++ b/mercurial/context.py	Fri Aug 15 02:46:44 2014 +0200
@@ -553,6 +553,8 @@
             anc = cahs[0]
         else:
             for r in self._repo.ui.configlist('merge', 'preferancestor'):
+                if r == '*':
+                    continue
                 ctx = changectx(self._repo, r)
                 anc = ctx.node()
                 if anc in cahs: