ubuntu hirsute replace sda1 (lubuntu) with gnome failed grub

[Chris Guiver]

Simple install of ubuntu hirsute daily (QA-test)
single partition only used; sda1 of
- dell [optiplex] 780 (c2q-q9400, 8gb, amd/ati cedar radeon hd 5000/6000/7350/8350)

manual partitioning, replace SDA1 (lubuntu daily; a couple of days old) with ubuntu daily

fails on install of grub?

ubuntu@ubuntu:/$ df -h
Filesystem Size Used Avail Use% Mounted on
tmpfs 783M 18M 765M 3% /run
/dev/sdb1 2.7G 2.7G 0 100% /cdrom
/cow 3.9G 119M 3.8G 4% /
/dev/disk/by-label/writable 4.7G 22M 4.5G 1% /var/log
tmpfs 3.9G 0 3.9G 0% /dev/shm
tmpfs 5.0M 8.0K 5.0M 1% /run/lock
tmpfs 4.0M 0 4.0M 0% /sys/fs/cgroup
tmpfs 3.9G 20K 3.9G 1% /tmp
tmpfs 783M 108K 783M 1% /run/user/999
/dev/sda1 658G 328G 297G 53% /target
/dev/sdb2 4.9M 4.9M 2.0K 100% /target/boot/efi
ubuntu@ubuntu:/$ df -h |grep target
/dev/sda1 658G 328G 297G 53% /target
/dev/sdb2 4.9M 4.9M 2.0K 100% /target/boot/efi

Why is it trying to write EFI partition to the THUMB-DRIVE?
I'm installing to /dev/sda

Duplicate of https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1923134 really

ProblemType: Bug
DistroRelease: Ubuntu 21.04
Package: ubiquity 21.04.14
ProcVersionSignature: Ubuntu 5.11.0-13.14-generic 5.11.7
Uname: Linux 5.11.0-13-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu62
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.461
CurrentDesktop: ubuntu:GNOME
Date: Wed Apr 14 10:11:30 2021
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash ---
LiveMediaBuild: Ubuntu 21.04 "Hirsute Hippo" - Beta amd64 (20210413)
ProcEnviron:
 LANGUAGE=en_AU.UTF-8
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_AU.UTF-8
 LC_NUMERIC=C.UTF-8
RebootRequiredPkgs:
 linux-image-5.11.0-13-generic
 linux-base
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)