Failed to install to /dev/sdc, tried to place booloader on sda instead

[Harel Amnon]

Booted from USB stick.
Chose to install on /dev/sdc
The installer complained that it fails to install grub, first on /dev/sda (which it wasn't supposed to touch!), and then also on /dev/sdc when I changed to that.

Ubuntu 18.04.3 LTS

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity 18.04.14.12
ProcVersionSignature: Ubuntu 5.0.0-23.24~18.04.1-generic 5.0.15
Uname: Linux 5.0.0-23-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.7
Architecture: amd64
CasperVersion: 1.394
Date: Wed Sep 11 13:32:38 2019
InstallCmdLine: file=/cdrom/preseed/ubuntu.seed boot=casper initrd=/casper/initrd quiet splash --- maybe-ubiquity
LiveMediaBuild: Ubuntu 18.04.3 LTS "Bionic Beaver" - Release amd64 (20190805)
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)