I have a cluster with three mongod instances,three config servers,and one mongos.
Something appears in the mongos log like this:

Thu Jul 25 10:01:39.607 [conn103] warning: mongos collstats doesn't know about: systemFlags
Thu Jul 25 10:01:39.607 [conn103] warning: mongos collstats doesn't know about: userFlags
Thu Jul 25 10:01:39.607 [conn103] warning: mongos collstats doesn't know about: systemFlags
Thu Jul 25 10:01:39.607 [conn103] warning: mongos collstats doesn't know about: userFlags
Thu Jul 25 10:01:40.422 [conn103] warning: mongos collstats doesn't know about: systemFlags
Thu Jul 25 10:01:40.422 [conn103] warning: mongos collstats doesn't know about: userFlags
Thu Jul 25 10:01:40.423 [conn103] warning: mongos collstats doesn't know about: systemFlags
Thu Jul 25 10:01:40.423 [conn103] warning: mongos collstats doesn't know about: userFlags
Thu Jul 25 10:01:41.106 [conn103] warning: mongos collstats doesn't know about: systemFlags
Thu Jul 25 10:01:41.107 [conn103] warning: mongos collstats doesn't know about: userFlags
Thu Jul 25 10:01:41.107 [conn103] warning: mongos collstats doesn't know about: systemFlags
Thu Jul 25 10:01:41.107 [conn103] warning: mongos collstats doesn't know about: userFlags
Thu Jul 25 10:01:41.698 [conn103] warning: mongos collstats doesn't know about: systemFlags
Thu Jul 25 10:01:41.699 [conn103] warning: mongos collstats doesn't know about: userFlags

I don't known what happens ,someone gives me an idea? Thanks for your attention!