When you run db.xyz.stats() via mongos it returns duplicate "ns" element. In my test the xyz collection itself was not sharded. Here's the output I got:

> var st = new ShardingTest("stest", 2, 0, 3);
> var mongos = st.s;
> var sdb = mongos.getDB("test")
> sdb.test.insert(

) // make sure collection exists
> sdb.test.stats()
{
"ns" : "test.test",
"sharded" : false,
"primary" : "shard0001",
"ns" : "test.test", // <=== duplicate "ns" element
"count" : 1,
"size" : 36,
"avgObjSize" : 36,
"storageSize" : 2048,
"numExtents" : 1,
"nindexes" : 1,
"lastExtentSize" : 2048,
"paddingFactor" : 1,
"flags" : 1,
"totalIndexSize" : 8192,
"indexSizes" :

,
"ok" : 1
}