grub installation to volume boot record fails

[glubsy]

I'm trying to install the grub bootloader through Ubiquity on an unencrypted partition (/dev/sda3) which is 20MBB. The /boot is supposed to be in the encrypted LUKS container along with /root (in /dev/sda4 mapped at /dev/mapper/root_crypt for example).

During ubiquityinstallation, I can select /dev/sda3 which is neat. However, it then crashes saying it failed to install grub on that particular partition (ext4). I don't see any output in terminal when starting ubiquity from there.
Error popup is: "Executin 'grub-install /dev/sda3' failed. This is a fatal error."

Suggestion: have the option NOT to install any bootloader at all, in the Bootloader installation drop-down menu (during manual install).
That way, users can manually install the grub bootloader anywhere they want, and add any additional arguments if necessary (--force for example, in case of a VBR).

ProblemType: Bug
DistroRelease: Ubuntu 16.10
Package: ubiquity 16.10.14 [modified: lib/partman/automatically_partition/question]
ProcVersionSignature: Ubuntu 4.8.0-22.24-generic 4.8.0
Uname: Linux 4.8.0-22-generic x86_64
ApportVersion: 2.20.3-0ubuntu8
Architecture: amd64
CasperVersion: 1.379
CurrentDesktop: KDE
Date: Tue Dec 20 16:23:17 2016
InstallCmdLine: file=/cdrom/preseed/kubuntu.seed boot=casper maybe-ubiquity initrd=/casper/initrd.lz quiet splash --- maybe-ubiquity
LiveMediaBuild: Kubuntu 16.10 "Yakkety Yak" - Release amd64 (20161012.1)
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

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