getLastError returning old/wrong/no data. The code that we are running works 100% when not sharded.

We have a 3 shard setup, each shard with 3 servers in a replica set. 3 config servers and 1 mongos running on the application server.

All querys are using safemode.

After going an update with a query that would match 0 documents the following is returned via getLastError()

"singleShard":"Set_01\/db1.test.co.uk,db5.test.co.uk,db9.test.co.uk",
"updatedExisting":true,
"n":1,
"lastOp":

{ "sec":1352302481, "inc":2 }

,
"connectionId":1392,
"err":null,
"ok":1

However, no documents will have been updated so n=1 should be wrong as well as updatedExsisting.

When using a query that does match a document ( and does successfully update), occasionally we will get the following from getLastError()

"singleShard":"Set_02\/db2.test.co.uk,db6.test.co.uk,db7.test.co.uk",
"n":0,
"lastOp":

{ "sec":1352295232, "inc":31 }

,
"connectionId":239,
"err":null,
"ok":1,
"writeback":

{ "$id":"509a633f0000000000000048" }

,
"instanceIdent":"mongo-01",
"updatedExisting":true,
"writebackGLE":{
"singleShard":"Set_02\/db2.test.co.uk,db6.test.co.uk,db7.test.co.uk",
"n":0,
"lastOp":

{ "sec":1352295232, "inc":31 }

,
"connectionId":239,
"err":null,
"ok":1
},
"initialGLEHost":"Set_01\/db1.test.co.uk,db5.test.co.uk,db9.test.co.uk"

"lastOp" is sometimes the same, if that means anything?