Comment 1 for bug 776850

No, this is incorrect, sorry. That code really does mean to be querying the properties of /, not /boot. While the change you suggest would happen to fix things in your case because your unencrypted /boot is also btrfs, it would fail in the case of ext2 /boot and an encrypted btrfs / - the value of rootflags needs to depend on the filesystem on /, not the filesystem on /boot.

I know you commented on bug 757631, but this can only be solved by fixing that bug, not in the way you suggest here.