Comment 1 for bug 1614971

To clarify, in OSC, we call the following:

   kwargs['tags'] = list(set(image.tags).union(set(parsed_args.tags)))
   try:
       image = image_client.images.update(image.id, **kwargs)
   ....

That seems to be enough to cause the regression

https://github.com/openstack/python-openstackclient/blob/master/openstackclient/image/v2/image.py#L833-L838