query = { "ref" : { "$in" : [ { "$ref" : "org.mongodb.morphia.query.QueryInForKeyTest$ReferencedEntity" , "$id" : { "$oid" : "5277efd33004acec38bffe48"}} , { "$ref" : "org.mongodb.morphia.query.QueryInForKeyTest$ReferencedEntity" , "$id" : { "$oid" : "5277efd33004acec38bffe49"}} , { "$ref" : "org.mongodb.morphia.query.QueryInForKeyTest$ReferencedEntity" , "$id" : { "$oid" : "5277efd33004acec38bffe4a"}} , { "$ref" : "org.mongodb.morphia.query.QueryInForKeyTest$ReferencedEntity" , "$id" : { "$oid" : "5277efd33004acec38bffe4b"}} , { "$ref" : "org.mongodb.morphia.query.QueryInForKeyTest$ReferencedEntity" , "$id" : { "$oid" : "5277efd33004acec38bffe4c"}} , { "$ref" : "org.mongodb.morphia.query.QueryInForKeyTest$ReferencedEntity" , "$id" : { "$oid" : "5277efd33004acec38bffe4d"}} , { "$ref" : "org.mongodb.morphia.query.QueryInForKeyTest$ReferencedEntity" , "$id" : { "$oid" : "5277efd33004acec38bffe4e"}} , { "$ref" : "org.mongodb.morphia.query.QueryInForKeyTest$ReferencedEntity" , "$id" : { "$oid" : "5277efd33004acec38bffe4f"}} , { "$ref" : "org.mongodb.morphia.query.QueryInForKeyTest$ReferencedEntity" , "$id" : { "$oid" : "5277efd33004acec38bffe50"}} , { "$ref" : "org.mongodb.morphia.query.QueryInForKeyTest$ReferencedEntity" , "$id" : { "$oid" : "5277efd33004acec38bffe51"}}]}} Failing jenkins job can be found here: https://jenkins.10gen.com/view/Java/job/morphia-test/jdk=HotSpot6,label=linux64,mongodb_configuration=single_server,mongodb_server=unstable-release/lastCompletedBuild/testReport/org.mongodb.morphia.query/QueryInForKeyTest/testInQueryByKey/