Comment 0 for bug 1299802

To reproduce (I've successfully reproduced the issue three
times in a row now, although sometimes one or other of the
unit agents does manage to upgrade successfully)

# deploy a 1.16 environment:
$ pwd
/home/rog/src/go/src/launchpad.net/juju-core/
$ bzr update -r juju-1.16.4
$ go install ./...
$ juju bootstrap
$ juju deploy wordpress
$ juju deploy mysql
$ juju add-relation wordpress mysql
# wait for services to start successfully
$ bzr update
$ bzr revision-info --tree
2509 tarmac-20140328183634-d639ea10wem30lfv
# use 1.18 as version number to avoid development-version
# logic.
$ ed version/version.go
/version = /s/".*"/"1.18.0"/
w
q
$ go install ./...
$ juju upgrade-juju --upload-tools
$

Sample status from the resulting environment is appended at the end of this description;
all-machines.log is attached.

The wordpress/0 unit has failed to come up.
Looking at the logs, it seems that the agent upgrades to 1.18,
but then the DesiredVersion API call returns 1.16 again
(this is weird), so it downgrades, but then the agent
configuration file is not compatible, because 1.18 config
files are not readable by 1.16 agents.

$ juju status
WARNING unknown config field "public-bucket"
WARNING unknown config field "public-bucket-region"
environment: sparse
machines:
  "0":
    agent-state: started
    agent-version: 1.18.0.1
    dns-name: ec2-54-82-187-161.compute-1.amazonaws.com
    instance-id: i-e383d6b2
    instance-state: running
    series: precise
    hardware: arch=amd64 cpu-cores=1 cpu-power=100 mem=1740M root-disk=8192M
  "1":
    agent-state: started
    agent-version: 1.18.0.1
    dns-name: ec2-54-82-25-135.compute-1.amazonaws.com
    instance-id: i-db88dd8a
    instance-state: running
    series: precise
    hardware: arch=amd64 cpu-cores=1 cpu-power=100 mem=1740M root-disk=8192M
  "2":
    agent-state: started
    agent-version: 1.18.0.1
    dns-name: ec2-54-80-24-48.compute-1.amazonaws.com
    instance-id: i-348cd965
    instance-state: running
    series: precise
    hardware: arch=amd64 cpu-cores=1 cpu-power=100 mem=1740M root-disk=8192M
services:
  mysql:
    charm: cs:precise/mysql-38
    exposed: false
    relations:
      cluster:
      - mysql
      db:
      - wordpress
    units:
      mysql/0:
        agent-state: started
        agent-version: 1.18.0.1
        machine: "2"
        public-address: ec2-54-80-24-48.compute-1.amazonaws.com
  wordpress:
    charm: cs:precise/wordpress-21
    exposed: false
    relations:
      db:
      - mysql
      loadbalancer:
      - wordpress
    units:
      wordpress/0:
        agent-state: down
        agent-state-info: (started)
        agent-version: 1.18.0.1
        machine: "1"
        open-ports:
        - 80/tcp
        public-address: ec2-54-82-25-135.compute-1.amazonaws.com