diff -r 312b861924c8 -r 0126e422450e mercurial/util.py
--- a/mercurial/util.py	Mon Jan 30 22:50:20 2017 +0900
+++ b/mercurial/util.py	Mon Jan 30 22:58:56 2017 -0800
@@ -550,7 +550,7 @@
         except ValueError:
             pass
     def keys(self):
-        return self._list
+        return self._list[:]
     def iterkeys(self):
         return self._list.__iter__()
     def iteritems(self):