Satellite 6.3 rename a host - Name has already been taken

I'm going about cleaning up some issues with our Satellite 6 install. After updating it to 6.3, I've been going through hosts that haven't reported. I noticed most of our hosts have the FQDN, but some have just the hostname. When attempting to add the domain to the hostname while editing a host I'm told that the Name has already been taken, but I cannot find it in the host list.

I know this is really just a superficial issue, but is there any way to do this, or should I be disassociating the host and re-adding?

Thanks.