grub-efi-amd64 fails to upgrade with mainline kernel installed

[hackel]

Got this while running a regular upgrade today (already on Ubuntu 18.04):

Setting up grub-efi-amd64 (2.02-2ubuntu8.3) ...
warning: file-aligned section .text extends beyond end of file
warning: checksum areas are greater than image size. Invalid section table?
E: Your kernels are unsigned. This system will fail to boot in a secure boot environment.
dpkg: error processing package grub-efi-amd64 (--configure):
 installed grub-efi-amd64 package post-installation script subprocess returned error exit status 1
Setting up libavfilter6:amd64 (7:3.4.4-0ubuntu0.18.04.1) ...
Setting up gnome-shell (3.28.3-0ubuntu0.18.04.2) ...
dpkg: dependency problems prevent configuration of grub-efi-amd64-signed:
 grub-efi-amd64-signed depends on grub-efi-amd64 | grub-pc; however:
  Package grub-efi-amd64 is not configured yet.
  Package grub-pc is not installed.

dpkg: error processing package grub-efi-amd64-signed (--configure):
 dependency problems - leaving unconfigured

This appears to be triggered because I have installed (and am running) linux-modules-4.18.3-041803-generic from the Ubuntu mainline kernels PPA. The kernel works just fine with secureboot enabled. It is required due to the extreme instability of the stock kernel on my XPS 13.

This appears to be related to #1786491. But why prevent the installation if it works just fine?
I also DO have the regular signed images (linux-generic and linux-oem) installed, so just because I have one unsigned kernel installed, it is borking up my whole system. In the middle of a stable release cycle, which seems insane to me.

I understand wanting to prevent someone from winding up with an unbootable system, but this patch is going far beyond that.

ProblemType: Package
DistroRelease: Ubuntu 18.04
Package: grub-efi-amd64 2.02-2ubuntu8.3
Uname: Linux 4.18.3-041803-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
Date: Thu Aug 23 16:54:56 2018
ErrorMessage: installed grub-efi-amd64 package post-installation script subprocess returned error exit status 1
InstallationDate: Installed on 2017-12-09 (257 days ago)
InstallationMedia: Ubuntu 17.10 "Artful Aardvark" - Release amd64 (20171018)
ProcCmdLine: BOOT_IMAGE=/vmlinuz-4.18.3-041803-generic root=/dev/mapper/ubuntu--vg-root ro
Python3Details: /usr/bin/python3.6, Python 3.6.5, python3-minimal, 3.6.5-3ubuntu1
PythonDetails: /usr/bin/python2.7, Python 2.7.15rc1, python-minimal, 2.7.15~rc1-1
RelatedPackageVersions:
 dpkg 1.19.0.5ubuntu2
 apt 1.6.3ubuntu0.1
SourcePackage: grub2
Title: package grub-efi-amd64 2.02-2ubuntu8.3 failed to install/upgrade: installed grub-efi-amd64 package post-installation script subprocess returned error exit status 1
UpgradeStatus: Upgraded to bionic on 2018-04-28 (117 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.