Comment 1 for bug 31719

No, it's not grub-install, it's a race condition in XFS. By the time you get round to running grub manually, XFS has settled down and managed to actually write everything to disk; if you had time to run grub manually as the installer's running grub-install, you'd see the same effect.

The question is, how long do we wait to let XFS settle? 15 seconds? 30 seconds? A minute? An hour? Who knows?