leave-on-terminate not working on host shutdown

Hi,

Im using this docker image on multiple AWS EC2 instances. I'm using the following consul.json file to pass the parameters to the container.

```
{
"leave_on_terminate": true,
"recursors": [
"10.1.2.2"
]
}
```

Docker run command below;

```
docker run -d --restart=always -p 8301:8301 -p 8301:8301/udp -p 8400:8400 -p 8500:8500 \
-p 53:53/udp -v /opt/consul:/data -v /var/run/docker.sock:/var/run/docker.sock \
-v /etc/consul:/etc/consul \
-h $(curl -s http://169.254.169.254/latest/meta-data/instance-id) \
--name consul-agent progrium/consul \
-advertise $(curl -s http://169.254.169.254/latest/meta-data/local-ipv4) \
-dc eu-west-1 -atlas={ATLAS_INFRASTRUCTURE} -atlas-join -atlas-token="{ATLAS_TOKEN}" \
-config-file /etc/consul/consul.json
```

If i do a "docker stop {CONTAINER_ID}" it sends the following and successfully removes the consul agent before termination.

```
==> Caught signal: terminated
==> Gracefully shutting down agent...
2015/08/04 07:42:30 [INFO] consul: client starting leave
2015/08/04 07:42:30 [INFO] serf: EventMemberLeave: i-99424134 10.1.2.64
2015/08/04 07:42:31 [INFO] agent: requesting shutdown
2015/08/04 07:42:31 [INFO] consul: shutting down client
2015/08/04 07:42:31 [INFO] agent: shutdown complete
```

However, if i do a linux shutdown on the host machine the same information is logged but it doesn't remove the consul agent from the cluster.

```
==> Caught signal: terminated
==> Gracefully shutting down agent...
2015/08/04 07:45:47 [INFO] consul: client starting leave
2015/08/04 07:45:48 [INFO] serf: EventMemberLeave: i-99424134 10.1.2.64
2015/08/04 07:45:48 [INFO] agent: requesting shutdown
2015/08/04 07:45:48 [INFO] consul: shutting down client
2015/08/04 07:45:48 [INFO] agent: shutdown complete
```

Not sure what could be causing this, maybe the network interface has been shutdown and the leave request doesn't get through to the cluster?

Any thoughts?

Cheers,

Jon