I have come across some strangeness with Ext4 and GRUB2.
I always install the bootloader in the root of my Linux partition and never the MBR - I use a third party utility for booting my OSs.
One distro I tried would allow me to select the Linux partition as the install destination for GRUB2 but would throw up an error. Fedora does not even give the option - it's the MBR or nothing. Apparently, the solution is to install GRUB2 manually with the --force parameter.
This does not seem to be a satisfactory solution for reasons I do not understand. Apparently there is insufficient room for GRUB2 in an ext4 file system. More info here https://bugzilla.redhat.com/show_bug.cgi?id=872826.
Does anybody have any idea when or if this issue will affect Mint?