diff -r 6122ad50e38f -r 8dda6f6ff564 mercurial/context.py
--- a/mercurial/context.py	Fri Aug 15 23:05:53 2014 +0900
+++ b/mercurial/context.py	Fri Aug 15 11:48:05 2014 -0500
@@ -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: