DHCP Relay works, but also getting denied at gateway?

Hey everyone, something weird is happening and I'd like to figure out why.

I have a Watchguard M300 firewall doing routing for internal traffic across VLANs. I have DHCP relay set up and working, but in the traffic monitor I'm seeing DHCP replies getting denied at the Watchguard's gateway IP on the client VLAN. Here's some specifics:

VLAN 10 — Servers — 10.0.10.0/24 (DHCP lives here) — Gateway IP 10.0.10.1

VLAN 20 — Ethernet Clients — 10.0.20.0/24 (laptop lives here) — Gateway IP 10.0.20.1

Now my laptop requests an IP and the Watchguard helpfully forwards the request and the laptop gets the DHCP response. However when this happens I also see a deny in the traffic logs from the DHCP server to the client gateway 10.0.20.1 on udp/67.

Why is anything being sent there, and why does it still work? Is it something I'm missing/doing wrong in my DHCP config? I have firewall policies configured to allow DHCP from the client VLAN to the DHCP server and vice versa.

Any suggestions are appreciated. I guess it's not urgent if it is working but you know the only thing scarier than things not working when they should is things working when they seemingly shouldn't.