Updated_at field on server not changed when associated security groups changes

I am accessing the nova api using the gophercloud SDK https://github.com/rackspace/gophercloud
I am running Openstack Newton installed with Openstack Ansible

I am accessing the “List Servers” call of the nova Api with the Changes-Since parameters for efficient polling
https://developer.openstack.org/api-guide/compute/polling_changes-since_parameter.html

However, the API is not working as expected.
When I stop or start a server instance, the API successfully detects the change in the server state and returns the server in the next call to ListServers with the Changes-Since parameter, as expected.
However when I attach a new security group to the server, the API does not detect and does not return the server in the next call to ListServers with the Changes-Since parameter.

Jay Pipes made a comment on a post I submited to the <email address hidden> list, saying this is caused because changes to which security groups are attached to a server instance do not set the "updated_at" field of the server instance.

I consider this a bug.
When querying the nova API using ListServer, the returned fields include the list of security groups attached to the server instances. Therefore the list of security group attached to an instance is part of the properties of the server instance. If that changes (attaching or detaching a security group) then the updated_at field should be updated to reflect a change in the properties of the server instance.

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