Running a lot of lxc-execute processes concurrently causes defunct processes, hangs forever

Ubuntu version:

Description: Ubuntu 12.04.2 LTS
Release: 12.04

lxc version:

lxc:
  Installed: 0.7.5-3ubuntu66
  Candidate: 0.7.5-3ubuntu66
  Version table:
 *** 0.7.5-3ubuntu66 0
        500 http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ precise-updates/universe amd64 Packages
        100 /var/lib/dpkg/status
     0.7.5-3ubuntu52 0
        500 http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ precise/universe amd64 Packages

Expected:

Expected it to work as normal, not hang.

What happened instead:

This is pretty easy to reproduce by running a bunch of processes (5 is fine to reproduce) that continuously execute very short lxc-execute processes (less than a second).

Here is a log from the process calling lxc-execute:

Feb 27 12:54:30 Running now: lxc-execute -n vm16946 -f /mnt/vm16946/lxc.conf -- sh /task/.runtask
Feb 27 12:54:30 Command executed, starting to read streams
Feb 27 12:54:30 out: hello

That's it, never exits/finishes. The program running inside lxc is a ruby program that prints "hello", that's all it does.

ps -ef shows this:

root 16090 16946 0 20:54 ? 00:00:00 lxc-execute -n vm16946 -f /mnt/vm16946/lxc.conf -- sh /task/.runtask
root 16100 16090 0 20:54 ? 00:00:00 [lxc-init] <defunct>

This never goes away and the parent process of lxc-execute hangs forever too.

On a side note, this same thing running on Quantal with lxc 0.8 rc1 will make the entire machine completely unresponsive so it actually gets worse in 0.8.