Issue with duplicate key ignorance

mongo-cl-driver-issue.lisp

TESTS> (defparameter *db* (make-instance 'mongo:database :name "pizzbook"))                                                                    
*DB*                                                                                                                                           
TESTS> (defparameter *test-collection* (mongo:collection *db* "the-test"))                                                                     
*TEST-COLLECTION*                                                                                                                              
TESTS> (mongo:insert-op *test-collection* (son "_id" "blah" "other" "field"))                                                                  
; No value                                                                                                                                     
TESTS> (mongo:insert-op *test-collection* (son "_id" "blah" "other" "another value"))                                                          
; No value                                                                                                                                                                                                                      
TESTS> (mongo:run-command *db* (son "getLastError" t))                                                                                         
{"err" => "E11000 duplicate key error index: pizzbook.the-test.$_id_  dup key: { : \"blah\" }", "code" => 11000, "n" => 0, "connectionId" => 4\
480, "ok" => 1.0d0}