I did have this problem from version 2.2 and then consecutively in 2.4 and now in 3.0. It seems I can't delete host or unlink and clear template. Unlinking the template works fine. I don't know what else I can't do with the host. For the moment solution for me to avoid false alarms for non-existent host is to disable it.
After I click button "Delete", there is a short time when browser waits for the server, and after that it displays only header with both menu bars but nothing underneath, clicking the hosts icon again - brings the supposedly "deleted" server back to the list.
There is no error in the server log.