Local DNS overrides no longer working with Dnsmasq after upgrading to 25.7.9

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A couple of days ago I upgraded from 25.7.7 (_4 or _6, can't remember exactly which) to 25.7.9, and immediately my local DNS overrides in Dnsmasq stopped resolving. I have an adguard server which is assigned via DHCP, and is configured with the OPNsense machine as the upstream for the local domain. Internet DNS lookups still work fine, however requests for the local DNS entries fail to resolve even when the OPNsense machine is queried directly.

I haven't been able to find anything wrong with the configuration (which has worked fine since I set it up a couple of months ago, and has continued to work through a couple of minor version upgrades until now). I tried reapplying the Dnsmasq settings (without any changes) to no effect.

In the Dnsmasq logs, post-upgrade (within minutes) I am now getting the message

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ignoring nameserver <OPNsense IP> - local interface
In my research so far it seems this is normally because the upstream of the DNS server has been set to itself, and this behaviour is to prevent infinitely looping DNS requests. But the upstream for this OPNsense machine is set to Quad9, so I'm not sure what's causing it. I tried changing the upstream in Settings-General to another provider, but this also had no effect. Have I run into a bug introduced with the 25.7.9 update?