Broken DNS in initramfs w/ a dual nic setup: "sed: /etc/resolv.conf: No such file or directory"

I have a system that has 2 NICs, one on a subnet w/ Internet access, the other a private network. Both networks are DHCP-configured, with only the Internet-enabled one providing DNS configuration.

I PXE booted subiquity (20.04.3 RC / 20210819.1), and it failed with the following on the console:

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[ 1.363173] Couldn't parse db signatures: -74
[ 1.370030] Couldn't parse dbx signatures: -74
Internet Systems Consortium DHCP Client 4.4.1
Copyright 2004-2018 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

BusyBox v1.30.1 (Ubuntu 1:1.30.1-4ubuntu6.3) built-in shell (ash)
Enter 'help' for a list of built-in commands.

(initramfs) Listening on LPF/enp1s0f1/0c:42:a1:49:ee:f5
Sending on LPF/enp1s0f1/0c:42:a1:49:ee:f5
Listening on LPF/enp1s0f0/0c:42:a1:49:ee:f4
Sending on LPF/enp1s0f0/0c:42:a1:49:ee:f4
Sending on Socket/fallback
DHCPDISCOVER on enp1s0f1 to 255.255.255.255 port 67 interval 3 (xid=0x2cc02d4b)
DHCPDISCOVER on enp1s0f0 to 255.255.255.255 port 67 interval 3 (xid=0x1801b37)
DHCPOFFER of 192.168.5.6 from 10.229.32.21
DHCPREQUEST for 192.168.5.6 on enp1s0f1 to 255.255.255.255 port 67 (xid=0x4b2dc02c)
DHCPOFFER of 10.229.72.169 from 10.229.32.21
DHCPREQUEST for 10.229.72.169 on enp1s0f0 to 255.255.255.255 port 67 (xid=0x371b8001)
DHCPACK of 192.168.5.6 from 10.229.32.21 (xid=0x2cc02d4b)
sed: /etc/resolv.conf: No such file or directory
bound to 192.168.5.6 -- renewal in 274 seconds.
wget: bad address 'cdimage.ubuntu.com'
Unable to find a live file system on the network

(initramfs)
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10.229.0.0 is the Internet-connected subnet. 192.168.5.0 is the private one. After a failure, I checked the contents of /etc/resolv.conf:

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(initramfs) cat /etc/resolv.conf
search maas. maas.
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Here's the grub.cfg entry I'm using:
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menuentry "Install Ubuntu Server" {
 set gfxpayload=keep
 linux /casper/vmlinuz quiet splash root=/dev/ram0 ramdisk_size=1500000 ip=dhcp url=http://cdimage.ubuntu.com/ubuntu-server/focal/daily-live/20210819.1/focal-live-server-arm64.iso ---
 initrd /casper/initrd
}
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If I disable the DHCP server on the private network, the installation is fine. I therefore assume I could also just specify the Internet-connected interface in the ip= setting as a workaround.