Possible Bug in DHCP Relay

I have decided to create a new thread as my problem has turned into what I believe is a bug:

I currently have a router-on-a-stick with the following config:

eth0.900 DHCP WAN
eth0.10 192.168.10.1/24 Management
eth0.20 192.168.20.1/24 Cameras
eth0.30 192.168.30.1/23 Staff
eth0.40. 192.168.40.1/23 Students

This is connected to a trunk port on my UniFi Switch (all VLANs are tagged).

My DHCP servers sit on vlan 10 behind the eth0.10 sub-interface

Currently, everything works just fine. DHCP Relay is configured to listen on eth0.10, eth0.20, eth0.30, and eth0.40.

I want to move Staff and Students vlan off of eth0 and move them to eth1 (eth1.30 and eth1.40).

Steps:

1. Delete eth0.30 and eth0.40
2. Create eth1.30 and eth1.40
3. Plug in the second uplink to the switch into eth1
4. Reconfigure DHCP Relay to listen on eth1.30 and eth1.40 (instead of eth0.30 and eth0.40, as these interfaces no longer exist).
5. Traffic still passes just fine. However, clients on vlan 30 and 40 no longer receive DHCP addresses.

I have tried using dnsmaq instead od ISC DHCP. No luck. I have tried rebooting the router and all my switches. No luck.