Grub fails to install - Debian Wheezy with mdadm RAID1 and GPT partition table

Looks like somehow Debian installer screws up the partition table. The "bios_grub" flag gets removed and becomes "raid" flag. The fix is to rework the partition table again with parted and set it back.

parted /dev/sda
set 1 bios_grub on
quit

Same for /dev/sdb, and then chrooting and installing grub with answer from this question: How can I fix/install/reinstall grub?