Scenario
As Primary user create PTR record, once created use List API as Admin user and
"x-auth-all-projects:True" in requests

Expected Result:
Primary PTR is listed in API response made by Admin user

Actual Result:
Received list is empty.

2021-07-13 16:27:14,965 869385 INFO [designate_tempest_plugin.tests.api.v2.test_ptrs] As Admin user, try to list PTR record for all projects by including "x-auth-all-projects" HTTP header.
2021-07-13 16:27:15,043 869385 INFO [tempest.lib.common.rest_client] Request (DesignatePtrRecord:test_list_floatingip_ptr_all_projects): 200 GET http://10.35.64.8/dns/v2/reverse/floatingips 0.077s
2021-07-13 16:27:15,044 869385 DEBUG [tempest.lib.common.rest_client] Request - Headers:

{'x-auth-all-projects': True, 'X-Auth-Token': '<omitted>'}

Body: None
Response - Headers:

{'date': 'Tue, 13 Jul 2021 13:27:14 GMT', 'server': 'Apache/2.4.41 (Ubuntu)', 'content-length': '86', 'x-openstack-request-id': 'req-9ae3bc4d-9876-4dd2-828b-a55576031f26', 'connection': 'close', 'content-type': 'application/json', 'status': '200', 'content-location': 'http://10.35.64.8/dns/v2/reverse/floatingips'}

Body: b'{"floatingips": [], "links": {"self": "http://10.35.64.8/dns/v2/reverse/floatingips"}}'

Note:
It's possible to reproduce using patchset #19 https://review.opendev.org/c/openstack/designate-tempest-plugin/+/794708