Comment 3 for bug 1868566

Okay, I just found out what is going on; Maybe should be taken into consideration, as, as is the "select default kernel entry" dropdown menu is broken :

What is wrong from grub-mkconfig script is $OS value, set to "Ubuntu", meanwhile the entries at boot have another name (for me, "Linux Mint 19 Xfce"). This looks like an old issue, with "Ubuntu" being hardcoded in a few files. Here is what gave me the tip, in /etc/default/grub.d/50_linuxmint.cfg :
 "danlo@BrixPyxis:$ more /etc/default/grub.d/50_linuxmint.cfg
#! /bin/sh
set -e

# Set distributor to "Ubuntu"
#
# In Mint 16:
# shim and grub come with hardcoded ubuntu strings upstream, without this EFI installation is broken
# https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1242417
#
# In Mint 17:
# Despite the bug report being marked as fixed, the situation is the same. Grub was patched by Ubuntu
# to assign the "ubuntu" distributor ID when it was given "Kubuntu". That results in Kubuntu finally
# getting EFI to work out of the box but still using "ubuntu" as far as grub-install is concerned.
# So we'll stick to "Ubuntu" for this iteration.
#
# In Mint 18:
# Some packages are still hardcoded with the "ubuntu" path.. fwupdate for instance.
# Visually, the grub boot menuentry name is set for derivatives in 10_linux,
# but underneath the EFI path remains "ubuntu" for everything to work properly.

GRUB_DISTRIBUTOR="Ubuntu"

-----------
=> $OS is still hardcoded to "Ubuntu" from GRUB_DISTRIBUTOR variable and Linux Mint seems to feed from a different source the texts on boot menu..!
Question is, where does Mint gets it's "Linux Mint 19 Xfce" from... I could not really find from reading 10_linux file.