First, I have to thank you again for the update, if you didn't notice, I did fork it, but haven't had time to really work on the ideas I was playing around with but I will make notes in my fork if you want to import any of them.
This issue though I think I need to address, unless you feel it's appropriate to add the extra boxes in the configuration page. I know the whole thing is supposed to stay as simple as possible, but for whatever reason, dnsmasq doesn't deliver the nameservers to the dhcp clients in my environment without the nameserver option being specified directly in the conf:
dhcp-option=6,8.8.8.8,8.8.4.4
This is probably due to the qnap not being the router in my network. The qnap is just another network device with subnetted access to the internet so only the qsync server is exposed.
I also use a few other flags for dhcp. So perhaps either not re-writing the entire conf when there is a config change, or adding a box for Additional Options to the config page.
I'm now using the 4.2.1 beta firmware because I needed to have an issue addressed by qnap, and they once again changed the entire webgui design, if you haven't seen it yet.
I'm unsure if your update, or if their update is the reason that dnsmasq icon doesn't show anywhere on the main menu or the desktop area, even when it's explicitly checked in the app menu.
(Complete uninstall and reinstall of the qpkg fixed this)
I'm sure the 4.2.1 will be rolled out publicly before March.
I also made some changes to the css style to alternate colors on the log file for readability. Those are in my fork.