Ensure-availability doesn't work after stopping non-leader

[Environment]

ii juju 1.20.10-0ubuntu1~14.04.1~juju1 all next generation service orchestration system
ii juju-core 1.20.10-0ubuntu1~14.04.1~juju1 amd64 Juju is devops distilled - client

ubuntu@niedbalski-bastion:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 14.04.1 LTS
Release: 14.04
Codename: trusty

$ juju bootstrap
$ juju ensure-availability ( 3 nodes )
$juju status

environment: niedbalski
machines:
  "0":
    agent-state: started
    agent-version: 1.20.10
    dns-name: 10.5.0.4
    instance-id: 5007ffe4-3f05-44d1-8dc5-4466adbda20a
    instance-state: ACTIVE
    series: trusty
    hardware: arch=amd64 cpu-cores=1 mem=2048M root-disk=20480M
    state-server-member-status: removing-vote
  "1":
    agent-state: started
    agent-version: 1.20.10
    dns-name: 10.5.0.5
    instance-id: c273df36-edd6-49ff-9f02-1919cbef989e
    instance-state: ACTIVE
    series: trusty
    hardware: arch=amd64 cpu-cores=1 mem=2048M root-disk=20480M
    state-server-member-status: has-vote
  "2":
    agent-state: started
    agent-version: 1.20.10
    dns-name: 10.5.0.6
    instance-id: 782258d6-6955-4565-aeab-8d042b7b9b1f
    instance-state: ACTIVE
    series: trusty
    hardware: arch=amd64 cpu-cores=1 mem=2048M root-disk=20480M
    state-server-member-status: has-vote

$ juju ssh 1
$ sudo service juju-machine-0 stop

Agent changes state to

machines:
  "0":
    agent-state: down
    agent-state-info: (started)
    agent-version: 1.20.10
    dns-name: 10.5.0.4
    instance-id: 5007ffe4-3f05-44d1-8dc5-4466adbda20a
    instance-state: ACTIVE
    series: trusty
    hardware: arch=amd64 cpu-cores=1 mem=2048M root-disk=20480M
    state-server-member-status: no-vote
  "1":
    agent-state: started
    agent-version: 1.20.10
    dns-name: 10.5.0.5
    instance-id: c273df36-edd6-49ff-9f02-1919cbef989e
    instance-state: ACTIVE
    series: trusty
    hardware: arch=amd64 cpu-cores=1 mem=2048M root-disk=20480M
    state-server-member-status: has-vote
  "2":
    agent-state: started
    agent-version: 1.20.10
    dns-name: 10.5.0.6
    instance-id: 782258d6-6955-4565-aeab-8d042b7b9b1f
    instance-state: ACTIVE
    series: trusty
    hardware: arch=amd64 cpu-cores=1 mem=2048M root-disk=20480M
    state-server-member-status: has-vote

Then i try to add a machine or run ensure-availaiblity again to remove the death node.

$juju add-machine

All the new machines keeps in 'pending' state forever

  "15":
    instance-id: pending
    series: trusty

$ juju ensure-availability

[Expected]

If the initial state 0 node is turned off ( jujud-machine-0 stop ) then juju add-machine/ensure-availability should works correctly.