Limit memory on a Docker container doesn't work

I am running the last version of Docker on top of Ubuntu 13.04 (Raring Ringtail):

root@docker:~# docker versionClient version: 0.6.6Go version (client): go1.2rc3Git commit (client): 6d42040Server version: 0.6.6Git commit (server): 6d42040Go version (server): go1.2rc3Last stable version: 0.6.6

But when I start the container,

root@docker:~# docker run -m=1524288 -i  -t ubuntu /bin/bashroot@7b09f638871a:/# free -m             total       used       free     shared    buffers     cachedMem:          1992        608       1383          0         30        341-/+ buffers/cache:        237       1755Swap:         2047          0       2047

I don't see any limiting from any kind, and my kernel has the cgroups memory limit enabled:

kernel /boot/vmlinuz-3.8.0-33-generic ro console=tty0 root=/dev/xvda1 cgroup_enable=memory swapaccount=1

What obvious thing am I missing here?