Dropping admin db sets FCV to 3.4 but leaves UUIDs

The following shows how dropping the admin db may leave UUIDs. test> db.adminCommand({getParameter: 1, featureCompatibilityVersion: 1}) { "featureCompatibilityVersion" : { "version" : "3.6" }, "ok" : 1 } test> use local switched to db local local> db.runCommand({listCollections: 1}) { "cursor" : { "id" : NumberLong(0), "ns" : "local.$cmd.listCollections", "firstBatch" : [ { "name" : "startup_log", "type" : "collection", "options" : { "capped" : true, "size" : 10485760 }, "info" : { "readOnly" : false, "uuid" : BinData(4,"8Vlh0RQDSSy2HRFJJlBVDQ==") }, "idIndex" : { "v" : 2, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "local.startup_log" } } ] }, "ok" : 1 } local> use admin switched to db admin admin> db.dropDatabase() { "dropped" : "admin", "ok" : 1 } admin> db.adminCommand({getParameter: 1, featureCompatibilityVersion: 1}) { "featureCompatibilityVersion" : { "version" : "3.4" }, "ok" : 1 } admin> use local switched to db local local> db.runCommand({listCollections: 1}) { "cursor" : { "id" : NumberLong(0), "ns" : "local.$cmd.listCollections", "firstBatch" : [ { "name" : "startup_log", "type" : "collection", "options" : { "capped" : true, "size" : 10485760 }, "info" : { "readOnly" : false, "uuid" : BinData(4,"8Vlh0RQDSSy2HRFJJlBVDQ==") }, "idIndex" : { "v" : 2, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "local.startup_log" } } ] }, "ok" : 1 } local> db.adminCommand({getParameter: 1, featureCompatibilityVersion: 1}) { "featureCompatibilityVersion" : { "version" : "3.4" }, "ok" : 1 } local> db.version() As shown, info.uuid is still present in the local.startup_log collection.