How to delete duplicate NIC entries (Error: Validation failed: Interfaces some interfaces are invalid) ?

Issue

• when MAC address of existing NIC interface changes, the entry in host details can get duplicated
• when trying to save any changes to the host details, it fails with error message:
  Some of the interfaces are invalid. Please check the table below.
• It is not possible to delete the duplicates from GUI, because attempts to save the host details with deleted NICs fail with the same error
• Can not register system with below error message.

  2016-12-16 13:04:19,438 [INFO] subscription-manager:16240:MainThread @connection.py:830 - Connection built: host=xxxx.local port=443 handler=/rhsm auth=none
2016-12-16 13:04:20,483 [ERROR] subscription-manager:16240:MainThread @managercli.py:1141 - Validation failed: Interfaces some interfaces are invalid
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/subscription_manager/managercli.py", line 1136, in _do_command
    content_tags=self.installed_mgr.tags)
  File "/usr/lib64/python2.7/site-packages/rhsm/connection.py", line 928, in registerConsumer
    return self.conn.request_post(url, params)
  File "/usr/lib64/python2.7/site-packages/rhsm/connection.py", line 697, in request_post
    return self._request("POST", method, params)
  File "/usr/lib64/python2.7/site-packages/rhsm/connection.py", line 611, in _request
    self.validateResponse(result, request_type, handler)
  File "/usr/lib64/python2.7/site-packages/rhsm/connection.py", line 661, in validateResponse
    raise RestlibException(response['status'], error_msg, response.get('headers'))
    RestlibException: Validation failed: Interfaces some interfaces are invalid