Can't mkdir /root (btrfs)

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http://unix.stackexchange.com – I performed a standard Debian install using wheezy/testing netinst iso for amd64. After the install completed I booted into a live environment so that I could snapshot the root as a btrfs subvolume named 'root'. To do so I renamed the /root directory to /rootuser temporarily however I am not able to move /rootuser back to /root in the new subvolume. I've seen other posts where people rename and move around the /root directory without any appearent issue. Is this a bug with btrfs? Here are the steps to replicate: Install Debian on btrfs (/dev/sda3, /dev/sda1=/boot (ext4), /dev/sda2=swap), (HowTos)