@Michael_Chare - Thanks for your reply. Yes, I've seen the list of devices the TG582N keeps, both through the web interface and the CLI - and I suspect you are correct. The "hostmgr list" command displays these devices and the sometimes *incorrect* associations the router makes between IP addresses and MAC addresses - this is what I think was screwing up the DNS entries.
If the *only* impact of disabling hostmgr is that the list of connected devices is no longer updated then I really don't care, I'm not sure what use it is anyway. The DHCP server still works as expected, the DNS server now actually *does* seem to work as expected. So if that's the only downside, I'm happy to leave hostmgr disabled. I was just hoping to get some confirmation of that.
Although I do know how to download, edit and upload the ini file, the changes I've made so far have all been through the CLI. Are you suggesting I change something else via the ini file?