Batch size becomes limit if sort is appended to it:

> db.test.insert(

{n: 1}

)
> db.test.insert(

{n: 2}

)
> db.test.insert(

{n: 3}

)
> db.test.insert(

{n: 4}

)
> db.test.insert(

{n: 5}

)

> db.test.find().batchSize(2).sort(

{n: 1}

)

{ "_id" : ObjectId("506e43b5681e3dfd1b92980b"), "n" : 1 } { "_id" : ObjectId("506e43b7681e3dfd1b92980c"), "n" : 2 }

> db.test.find().batchSize(2)

{ "_id" : ObjectId("506e43b5681e3dfd1b92980b"), "n" : 1 } { "_id" : ObjectId("506e43b7681e3dfd1b92980c"), "n" : 2 } { "_id" : ObjectId("506e43b8681e3dfd1b92980d"), "n" : 3 } { "_id" : ObjectId("506e43b9681e3dfd1b92980e"), "n" : 4 } { "_id" : ObjectId("506e43ba681e3dfd1b92980f"), "n" : 5 }

The problem seems to be in the server. I can reproduce the same issue with the Go driver.