test cases "test_list_flavors_detailed_filter_by_min_disk" and "test_list_flavors_filter_by_min_disk" only work if "flavor_ref" set to the minimum flavor

my flavor list:

+----+-----------+-----------+------+----------+-------+-------------+
| ID | Name | Memory_MB | Swap | Local_GB | VCPUs | RXTX_Factor |
+----+-----------+-----------+------+----------+-------+-------------+
| 2 | m1.small | 2048 | | 10 | 1 | 1.0 |
| 3 | m1.medium | 4096 | | 10 | 2 | 1.0 |
| 4 | m1.large | 8192 | | 10 | 4 | 1.0 |
| 5 | m1.xlarge | 16384 | | 10 | 8 | 1.0 |
| 6 | testing | 512 | | 0 | 1 | 1.0 |
+----+-----------+-----------+------+----------+-------+-------------+

i set flavor_ref=6 in etc/tempest.conf, test cases are working fine:

The list of flavors should be filtered by disk space ... ok
The list of flavors should be filtered by RAM ... ok

now i remove the flavor with id 6 and i set flavor_ref=2 in etc/tempest.conf, test cases are now failing:

+----+-----------+-----------+------+----------+-------+-------------+
| ID | Name | Memory_MB | Swap | Local_GB | VCPUs | RXTX_Factor |
+----+-----------+-----------+------+----------+-------+-------------+
| 2 | m1.small | 2048 | | 10 | 1 | 1.0 |
| 3 | m1.medium | 4096 | | 10 | 2 | 1.0 |
| 4 | m1.large | 8192 | | 10 | 4 | 1.0 |
| 5 | m1.xlarge | 16384 | | 10 | 8 | 1.0 |
+----+-----------+-----------+------+----------+-------+-------------+

======================================================================
FAIL: The detailed list of flavors should be filtered by disk space
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/berendt/Documents/repositories/tempest/tempest/tests/test_flavors.py", line 97, in test_list_flavors_detailed_filter_by_min_disk
    self.assertFalse(any([i for i in flavors if i['id'] == flavor_id]))
AssertionError: True is not False

======================================================================
FAIL: The list of flavors should be filtered by disk space
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/berendt/Documents/repositories/tempest/tempest/tests/test_flavors.py", line 121, in test_list_flavors_filter_by_min_disk
    self.assertFalse(any([i for i in flavors if i['id'] == flavor_id]))
AssertionError: True is not False

----------------------------------------------------------------------
Ran 13 tests in 2.614s

FAILED (failures=2)