Cross-bucket N1QL queries fail even with "add_bucket_creds"

from couchbase.bucket import Bucket

from couchbase.n1ql import N1QLQuery

cb = Bucket("couchbase://172.23.100.55/bucket-1", password="password")

cb.add_bucket_creds("bucket-1", "password")

cb.add_bucket_creds("bucket-2", "password")

cb.add_bucket_creds("bucket-3", "password")

q = N1QLQuery("SELECT u.email AS email, COUNT(t.title) "

              "FROM `bucket-2` t "

              "INNER JOIN `bucket-3` c ON KEYS t.categories "

              "LEFT OUTER JOIN `bucket-1` u ON KEYS t.owner "

              "WHERE t.capped = $1 AND c.name = $2 "

              "GROUP BY u.email", "d8576d", "n1ql-000000000001")

q.adhoc = False

q.consistency = 'not_bounded'

cb.n1ql_query(q).execute()

couchbase.exceptions.HTTPError: <RC=0x3B[HTTP Operation failed. Inspect status code for details], HTTP Request failed. Examine 'objextra' for full result, Results=1, C Source=(src/http.c,140), OBJ=ViewResult<rc=0x3B[HTTP Operation failed. Inspect status code for details], value={u'status': u'stopped', u'errors': [{u'msg': u'Authorization Failed Keyspace bucket-2', u'code': 10000}], u'results': [], u'metrics': {u'elapsedTime': u'6.651541ms', u'executionTime': u'6.579298ms', u'resultSize': 0, u'resultCount': 0, u'errorCount': 1}, u'requestID': u'4578d546-d2e0-4d6e-8ce7-575e8177ebe7', u'signature': {u'email': u'json', u'$1': u'number'}}, http_status=401>>