This is possibly explained by the following comments from LP:1775227:
https://bugs.launchpad.net/ubuntu/+source/horizon/+bug/1775227/comments/5 https://bugs.launchpad.net/ubuntu/+source/horizon/+bug/1775227/comments/6
"I agree that the current horizon does not support role create/delete operations by domain admin."
This is possibly explained by the following comments from LP:1775227:
https:/ /bugs.launchpad .net/ubuntu/ +source/ horizon/ +bug/1775227/ comments/ 5 /bugs.launchpad .net/ubuntu/ +source/ horizon/ +bug/1775227/ comments/ 6
https:/
"I agree that the current horizon does not support role create/delete operations by domain admin."