--- a/mercurial/manifest.py	Sat Jul 01 19:35:17 2017 -0700
+++ b/mercurial/manifest.py	Fri Jun 30 01:47:48 2017 +0900
@@ -1230,7 +1230,8 @@
             self._dirlogcache = {'': self}
 
         super(manifestrevlog, self).__init__(opener, indexfile,
-                                             checkambig=bool(dir))
+                                             # only root indexfile is cached
+                                             checkambig=not bool(dir))
 
     @property
     def fulltextcache(self):