$db values for DBRef datatype does not seem to persist in mongo collection

1) Create a collection named 'people' in database 'kamal' and insert a doc as db.people.insert({_id : ObjectId('5191cc6684ae75ea07e4ef3b'), "name" : "Tu"}) 2) Now in another database, insert a document into collection named 'halloa' as follows: db.halloa.insert({"name" : "dukur", "myref" : {"$ref" : "people", "$id" : "5191cc6684ae75ea07e4ef3b", "$db" : "kamal"} }) 3) Retrieve the document using following query: db.halloa.find( {"name" : "dukur"} )