Comment 10 for bug 1021471

Looking around for this bug, after getting it myself a few more times... I found http://lists.debian.org/debian-kernel/2012/05/msg00494.html which mentions a similar behaviour.

I extracted the C example and built it: http://paste.ubuntu.com/1182799/

Running it, indeed triggered the issue here, any subsequent call to lxc-start will just hang.
When running lxc-start under strace, I'm getting:
stat("/home/stgraber/data/vm/lxc/lib/precise-gui-i386/rootfs", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
open("/home/stgraber/data/vm/lxc/lib/precise-gui-i386/rootfs.hold", O_RDWR|O_CREAT, 0600) = 17
clone(

So it looks like, whatever the issue is, it's triggering when trying to clone(CLONE_NEWNET).

Hope that helps point towards the right direction.