A server started with --replSet <name> return this ambiguous ismaster response in both the uninitialized and shunned state; shunned is when the node was removed from the replica set configuration:

{ "serverUsed" : "localhost:27017" ,
  "ismaster" : false ,
  "secondary" : false ,
  "info" : "can't get local.system.replset config from self or any seed (EMPTYCONFIG)" ,
  "isreplicaset" : true ,
  "maxBsonObjectSize" : 16777216 ,
  "maxMessageSizeBytes" : 48000000 ,
  "localTime" : { "$date" : "2014-04-01T14:10:05.110Z"} ,
  "ok" : 1.0 }

Note: isreplicaset exists in only these states and there is no hosts field, nor setName nor setVersion to work with.

It would be very helpful for clients and drivers to be able to uniquely identify each state with as much context as possible so that replica set discovery/monitoring behavior can be well defined.