Hi,
Can you please provide some more details. I tried to reproduce but did not see the issue you reported:

openstack@openstack:~/devstack$ quantum floatingip-list
+--------------------------------------+------------------+---------------------+--------------------------------------+
| id                                   | fixed_ip_address | floating_ip_address | port_id                              |
+--------------------------------------+------------------+---------------------+--------------------------------------+
| dab238eb-dfcc-4b97-88ac-1fbe2dc35357 | 10.0.0.3         | 172.24.4.227        | 04d995fa-bcb4-4fad-963f-71ccc7db6aa5 |
+--------------------------------------+------------------+---------------------+--------------------------------------+

+--------------------------------------+------+-------------------+---------------------------------------------------------------------------------+
| id                                   | name | mac_address       | fixed_ips                                                                       |
+--------------------------------------+------+-------------------+---------------------------------------------------------------------------------+
| 04d995fa-bcb4-4fad-963f-71ccc7db6aa5 |      | fa:16:3e:63:76:12 | {"subnet_id": "85d39b8f-7e43-44fd-8b83-ea96d46cf2b2", "ip_address": "10.0.0.3"} |
| 3f7acba7-cfaa-46be-89f6-365c9862299e |      | fa:16:3e:17:80:da | {"subnet_id": "85d39b8f-7e43-44fd-8b83-ea96d46cf2b2", "ip_address": "10.0.0.2"} |
| b950394d-5db6-4efb-b5bc-ba6f7cf0222b |      | fa:16:3e:3a:04:30 | {"subnet_id": "85d39b8f-7e43-44fd-8b83-ea96d46cf2b2", "ip_address": "10.0.0.1"} |
+--------------------------------------+------+-------------------+---------------------------------------------------------------------------------+

===> delete the VM

openstack@openstack:~/devstack$ quantum floatingip-list
+--------------------------------------+------------------+---------------------+---------+
| id                                   | fixed_ip_address | floating_ip_address | port_id |
+--------------------------------------+------------------+---------------------+---------+
| dab238eb-dfcc-4b97-88ac-1fbe2dc35357 |                  | 172.24.4.227        |         |
+--------------------------------------+------------------+---------------------+---------+
openstack@openstack:~/devstack$ 
openstack@openstack:~/devstack$ 

openstack@openstack:~/devstack$ quantum port-list (demo user)
+--------------------------------------+------+-------------------+---------------------------------------------------------------------------------+
| id                                   | name | mac_address       | fixed_ips                                                                       |
+--------------------------------------+------+-------------------+---------------------------------------------------------------------------------+
| 3f7acba7-cfaa-46be-89f6-365c9862299e |      | fa:16:3e:17:80:da | {"subnet_id": "85d39b8f-7e43-44fd-8b83-ea96d46cf2b2", "ip_address": "10.0.0.2"} |
| b950394d-5db6-4efb-b5bc-ba6f7cf0222b |      | fa:16:3e:3a:04:30 | {"subnet_id": "85d39b8f-7e43-44fd-8b83-ea96d46cf2b2", "ip_address": "10.0.0.1"} |
+--------------------------------------+------+-------------------+---------------------------------------------------------------------------------+


openstack@openstack:~/devstack$ 
openstack@openstack:~/devstack$ 
openstack@openstack:~/devstack$ 
openstack@openstack:~/devstack$ quantum port-list  (admin user)
+--------------------------------------+------+-------------------+-------------------------------------------------------------------------------------+
| id                                   | name | mac_address       | fixed_ips                                                                           |
+--------------------------------------+------+-------------------+-------------------------------------------------------------------------------------+
| 3f7acba7-cfaa-46be-89f6-365c9862299e |      | fa:16:3e:17:80:da | {"subnet_id": "85d39b8f-7e43-44fd-8b83-ea96d46cf2b2", "ip_address": "10.0.0.2"}     |
| ac5973aa-a300-4d60-ac3f-a52bbcfdb5a6 |      | fa:16:3e:a9:5a:29 | {"subnet_id": "b0b1d9e1-0262-4f3c-9427-35ae095e0b8b", "ip_address": "172.24.4.227"} |
| b950394d-5db6-4efb-b5bc-ba6f7cf0222b |      | fa:16:3e:3a:04:30 | {"subnet_id": "85d39b8f-7e43-44fd-8b83-ea96d46cf2b2", "ip_address": "10.0.0.1"}     |
| fbcc0848-00b3-4f26-84ff-2aca1eb45fe8 |      | fa:16:3e:02:e4:ee | {"subnet_id": "b0b1d9e1-0262-4f3c-9427-35ae095e0b8b", "ip_address": "172.24.4.226"} |
+--------------------------------------+------+-------------------+-------------------------------------------------------------------------------------+
openstack@openstack:~/devstack$ 

The floating ip port exists as long as the floating ip is defined.

Can you please provide some additional information that I missed.

Thanks
Gary