Comment 20 for bug 1059827

There is no need to reformat with Ext4. If you wish to use BtrFS for the Boot partition, it's recommended. Just tell the partitioner to start at the 1MB boundary instead of the first sector. To reiterate, you need an empty 1MB at the beginning of your drive to write to. I would call this an error with the partitioner/Ubuntu Installer instead of Grub2.
To do this properly, start GParted and format it using this method.