Same problem.
Ubuntu 12.04 LTS Beta 1 - 64 bits Fresh install on btrfs formatted from Ubiquity
$ mount /dev/sda1 on / type btrfs (rw,subvol=@)
Linux maria 3.2.0-23-lowlatency #31-Ubuntu SMP PREEMPT Wed Apr 11 02:24:03 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
Same problem.
Ubuntu 12.04 LTS Beta 1 - 64 bits
Fresh install on btrfs formatted from Ubiquity
$ mount
/dev/sda1 on / type btrfs (rw,subvol=@)
Linux maria 3.2.0-23-lowlatency #31-Ubuntu SMP PREEMPT Wed Apr 11 02:24:03 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux