Comment 6 for bug 1214085

Additional note: I've found the problem manifests more easily with the following modified test script (this one forks all LXC clone/start operations immediately):

test.sh:

    #!/usr/bin/env bash

    prefix=$1

    test -z "${prefix}" && echo 'error: missing required parameter: prefix' 1>&2 && exit 1

    path=/mnt/test

    sudo lxc-destroy -n c1 2>/dev/null
    sudo lxc-create -t ubuntu -B btrfs -n c1

    for i in `seq 1 20`; do
        echo $(sudo lxc-clone -s -B btrfs -P $path -o c1 -n $prefix$i; sudo lxc-start -d -n $prefix$i) &
    done

    sleep 10

    # Create even more.
    for i in `seq 21 40`; do
        echo $(sudo lxc-clone -s -B btrfs -P $path -o c1 -n $prefix$i; sudo lxc-start -d -n $prefix$i) &
    done