This problem is not limited to btrfs subvolumes. The same bug also affects at least ZFS mount points: bug 1390828, samba network mounts: bug 457047, --bind mounted directories: bug 594674, NFS mounts same bug comment 13 and tmpfs mounts same bug comment 8.
Increasing importance from low to medium as the root problem ends up affecting a much wider set of installations than initially thought.
I can confirm the problem for btrfs subvolumes.
This problem is not limited to btrfs subvolumes. The same bug also affects at least ZFS mount points: bug 1390828, samba network mounts: bug 457047, --bind mounted directories: bug 594674, NFS mounts same bug comment 13 and tmpfs mounts same bug comment 8.
Increasing importance from low to medium as the root problem ends up affecting a much wider set of installations than initially thought.