I had the same problem with grub-install failing with "unknown filesystem".
The solution is to either create a seperate (300M - 1G) filesystem for /boot and format it as ext3, or use ext3 for your root filesystem.
Grub is apparently unable to use ext4 filesystems depending on what options the filesystem is using. More details can be found at https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=866603
Hello ! Same for me.
I installed it on virtual and physical machine and the system won't boot.
For me the grub been installed to the MBR, but the system dont want boot.
There is a bug in the grub package.