Michael Hudson-Doyle

This will be caused by layering nonsense, if you install something into the minimal layer that updates /var/lib/dpkg/status in the minimal layer, but the next layer has its own /var/lib/dpkg/status...

I was going to respond to each comment but I think perhaps it's best for me to wait until you ping again?

Hm, yes probably. unmkinitramfs is just a shell script, I could probably bundle it for use on non-Debian/Ubuntu systems.

That's a bit odd indeed. It could be running out of space, I guess total peak consumption might be several multiples of the squashfs but I wouldn't expect it to...

Yeah, I don't think replace-kernel has ever worked on desktop ISOs unfortunately.

No blocker I'm aware of, it'll just be fiddly and annoying I expect.