copyCollection cannot append namespaces with options

Example: db.runCommand({cloneCollection: 'mydb.map', from:'[source address]', query: { _id: 'TDL-TRIPWL-2013' }}); { "ok" : 1 } Above works even though .map collection exists. db.runCommand({cloneCollection: 'mydb.category', from:'[source address]', query: { event_name: 'TDL-TRIPWL-2013' }}); { "ok" : 0, "errmsg" : "collection already exists" } But this does not...what is the difference? I thought maybe it's the use of _id.. but this didn't work either: db.runCommand({cloneCollection: 'mydb.category', from:'[source address]', query: { _id: ObjectId("5154d54aecfdf41427000041") }}); { "ok" : 0, "errmsg" : "collection already exists" } Info on my 2 collections: { "ns" : "rt01.map", "count" : 9, "size" : 7840, "avgObjSize" : 871.1111111111111, "storageSize" : 36864, "numExtents" : 1, "nindexes" : 1, "lastExtentSize" : 36864, "paddingFactor" : 1.0020000000000011, "systemFlags" : 1, "userFlags" : 0, "totalIndexSize" : 8176, "indexSizes" : { "_id_" : 8176 }, "ok" : 1 }   { "ns" : "rt01.category", "count" : 575, "size" : 233208, "avgObjSize" : 405.5791304347826, "storageSize" : 696320, "numExtents" : 4, "nindexes" : 3, "lastExtentSize" : 524288, "paddingFactor" : 1.5120000000000196, "systemFlags" : 1, "userFlags" : 0, "totalIndexSize" : 130816, "indexSizes" : { "_id_" : 32704, "name_1_event_name_1" : 49056, "event_name_1_name_1" : 49056 }, "ok" : 1 }