panic while setting a config value

$ juju version
1.13.0-saucy-amd64

$ which juju
/home/sidnei/src/go/bin/juju

~/src/go/src/launchpad.net/juju-core$ bzr info
Lightweight checkout (format: 2a)
Location:
  light checkout root: .
   checkout of branch: .bzr/cobzr/master
    shared repository: .bzr/cobzr

Related branches:
  parent branch: bzr+ssh://bazaar.launchpad.net/+branch/juju-core/

$ bzr revno
1544

$ juju get u1-public-gallery -e local

charm: ubuntuone-servers
service: u1-public-gallery
settings:
  api_server.s3_bucket:
    default: true
    description: 'Bucket used to store file contents.

'
    type: string
    value: ubuntuone-storage
  aws_s3.host:
    default: true
    description: 'Amazon S3 endpoint.

'
    type: string
    value: s3.amazonaws.com
  aws_s3.port:
    default: true
    description: 'Amazon S3 port to use.

'
    type: int
    value: 443
  aws_s3.proxy_host:
    default: true
    description: 'Proxy host to use for talking to Amazon S3.

'
    type: string
    value: ""
  aws_s3.proxy_port:
    default: true
    description: 'Proxy port to use for talking to Amazon S3.

'
    type: int
    value: 0
  aws_s3.use_ssl:
    default: true
    description: 'Use ssl when talking to Amazon S3.

'
    type: boolean
    value: true
  config.prototype.increment_options:
    default: true
    description: 'Which options to increment when using the prototype overlay.

'
    type: string
    value: ""
  dependencies_package:
    description: 'Dependencies package that should be installed.

'
    type: string
    value: ubuntuone-appserver-dependencies
  general.environment_name:
    default: true
    description: 'Environment that we''re running.

'
    type: string
    value: ""
  general.files_store:
    default: true
    description: 'Storage backend to use for files.

'
    type: string
    value: s3
  general.port:
    default: true
    description: 'Base port to listen on.

'
    type: int
    value: 8080
  general.service_name:
    default: true
    description: 'Name of the service that will be configured.

'
    type: string
    value: appserver
  host_environment_name:
    default: true
    description: 'Host environment we''re running on. Used as the prefix to select
      which configuration will be used by the underlying service (eg ''dc_production_updown-lazr.conf'').

'
    type: string
    value: dc
  keystone.host:
    default: true
    description: 'Keystone endpoint host.

'
    type: string
    value: keystone.canonistack.canonical.com
  keystone.path:
    default: true
    description: 'Keystone path to use when building the URL.

'
    type: string
    value: /v2.0
  keystone.port:
    default: true
    description: 'Keystone endpoint port to use.

'
    type: int
    value: 443
  keystone.proxy_host:
    default: true
    description: 'Proxy host to use for talking to Keystone/Swift.

'
    type: string
    value: ""
  keystone.proxy_port:
    default: true
    description: 'Proxy port to use for talking to Keystone/Swift.

'
    type: int
    value: 0
  keystone.region:
    default: true
    description: 'Keystone region to use.

'
    type: string
    value: lcy02
  keystone.use_ssl:
    default: true
    description: 'Use ssl when talking to Keystone/Swift.

'
    type: boolean
    value: true
  log_rsync_host:
    default: true
    description: 'Rsync host for application logs

'
    type: string
    value: ""
  nagios_check_http_params:
    description: 'The parameters to pass to the nrpe plugin check_http.

'
    type: string
    value: -I 127.0.0.1 -p 8080 -u /?status=1 -s \\'I am Alive\\'
  nagios_context:
    default: true
    description: "Used by the nrpe-external-master subordinate charm. A string that
      will be prepended to instance name to set the host name in nagios. So for instance
      the hostname would be something like:\n juju-postgresql-0\nIf you're running
      multiple environments with the same services in them this allows you to differentiate
      between them.\n"
    type: string
    value: juju
  new_user_shards:
    default: true
    description: 'Comma-separated list of shards to create new users on.

'
    type: string
    value: ""
  pgpass:
    default: true
    description: 'Contents of .pgpass to be used for the service.

'
    type: string
    value: ""
  secrets:
    default: true
    description: 'Secrets file override to be used for the service.

'
    type: string
    value: ""
  session.cookie_domain:
    default: true
    description: 'Domain to be used for cookie setting.

'
    type: string
    value: .staging.one.ubuntu.com
  session.cookie_secure:
    default: true
    description: 'Only set cookie for secure connections.

'
    type: boolean
    value: true
  shards:
    default: true
    description: 'Number of storage shards to configure.

'
    type: int
    value: 1
  sitenames:
    description: 'Site names (really, domain names) that map to this service when
      reverse-proxying via squid.

'
    type: string
    value: photo-gallery-public
  sources_list:
    default: true
    description: 'Custom repository entry to fetch packages from.

'
    type: string
    value: ""
  swift.container:
    default: true
    description: 'Swift container to use for storage.

'
    type: string
    value: test
  swift.fallback_container:
    default: true
    description: 'Swift container to use as fallback if object not found in default
      container.

'
    type: string
    value: ""
  template:
    description: 'Supervisor config template to use.

'
    type: string
    value: wsgi.appserver
  threads.max_requests:
    default: true
    description: 'How many worker threads per wsgi process to run.

'
    type: int
    value: 4
  twisted_wsgi.ports:
    default: true
    description: 'How many ports to open up on the parent wsgi process.

'
    type: int
    value: 1
  twisted_wsgi.processes:
    default: true
    description: 'How many wsgi worker processes to run.

'
    type: int
    value: 4
  url.base:
    default: true
    description: 'Base application frontend URL.

'
    type: string
    value: https://staging.one.ubuntu.com
  url.click_down_private:
    default: true
    description: 'URL for click packages private download service.

'
    type: string
    value: https://private.apps.staging.ubuntu.com
  url.click_down_public:
    default: true
    description: 'URL for click packages public download service.

'
    type: string
    value: https://public.apps.staging.ubuntu.com
  url.click_up:
    default: true
    description: 'URL for click packages upload service.

'
    type: string
    value: https://upload.apps.staging.ubuntu.com
  url.media:
    default: true
    description: 'URL for media resources (css, images, etc).

'
    type: string
    value: https://media.staging.one.ubuntu.com
  url.openid_sso_server:
    default: true
    description: 'URL for OpenID/SSO service.

'
    type: string
    value: https://login.staging.ubuntu.com
  url.streaming:
    default: true
    description: 'URL for music streaming service.

'
    type: string
    value: https://streaming.staging.one.ubuntu.com
  url.u1ms_search_base:
    default: true
    description: 'URL for music search service endpoint.

'
    type: string
    value: http://musicsearch.staging.ubuntu.com/v1/search
  url.updown:
    default: true
    description: 'URL for web-based files upload/download service.

'
    type: string
    value: https://files.staging.one.ubuntu.com

$ juju set u1-public-gallery general.environment_name=staging -e local
panic: runtime error: comparing uncomparable type map[string]interface {}

goroutine 1 [running]:
launchpad.net/juju-core/state.(*Settings).Write(0xc2003d7ea0, 0xc200313780, 0x7fff30ea4270, 0x18, 0x8e1e80, ...)
 /home/sidnei/src/go/src/launchpad.net/juju-core/state/settings.go:138 +0x285
launchpad.net/juju-core/state.(*Service).UpdateConfigSettings(0xc200371280, 0xc200313340, 0xc20036cb80, 0x0)
 /home/sidnei/src/go/src/launchpad.net/juju-core/state/service.go:768 +0x1be
main.(*SetCommand).Run(0xc2001e51c0, 0xc2001e55c0, 0x0, 0x0)
 /home/sidnei/src/go/src/launchpad.net/juju-core/cmd/juju/set.go:88 +0x1dd
launchpad.net/juju-core/cmd.(*SuperCommand).Run(0xc2001df850, 0xc2001e55c0, 0xc2001e55c0, 0x0)
 /home/sidnei/src/go/src/launchpad.net/juju-core/cmd/supercommand.go:233 +0xde
launchpad.net/juju-core/cmd.Main(0xc2001e5600, 0xc2001df850, 0xc2001e55c0, 0xc20012c010, 0x5, ...)
 /home/sidnei/src/go/src/launchpad.net/juju-core/cmd/cmd.go:162 +0x279
main.Main(0xc20012c000, 0x6, 0x6)
 /home/sidnei/src/go/src/launchpad.net/juju-core/cmd/juju/main.go:96 +0x15fe
main.main()
 /home/sidnei/src/go/src/launchpad.net/juju-core/cmd/juju/main.go:100 +0x42

goroutine 2 [syscall]:

goroutine 8 [sleep]:
time.Sleep(0x1dcd6500)
 /usr/local/go/src/pkg/runtime/ztime_linux_amd64.c:19 +0x2f
labix.org/v2/mgo.(*mongoCluster).syncServersLoop(0xc20015eb60)
 /home/sidnei/src/go/src/labix.org/v2/mgo/cluster.go:326 +0x1ec
created by labix.org/v2/mgo.newCluster
 /home/sidnei/src/go/src/labix.org/v2/mgo/cluster.go:69 +0xf8

goroutine 6 [IO wait]:
net.runtime_pollWait(0x7fe61a4d7f00, 0x72, 0x0)
 /usr/local/go/src/pkg/runtime/znetpoll_linux_amd64.c:118 +0x82
net.(*pollDesc).WaitRead(0xc200200620, 0xb, 0xc20014e3f0)
 /usr/local/go/src/pkg/net/fd_poll_runtime.go:75 +0x31
net.(*netFD).Read(0xc2002005a0, 0xc200380000, 0x1000, 0x1000, 0x0, ...)
 /usr/local/go/src/pkg/net/fd_unix.go:195 +0x2b3
net.(*conn).Read(0xc200000c28, 0xc200380000, 0x1000, 0x1000, 0x0, ...)
 /usr/local/go/src/pkg/net/net.go:123 +0xc3
bufio.(*Reader).fill(0xc2001e4ba0)
 /usr/local/go/src/pkg/bufio/bufio.go:79 +0x10c
bufio.(*Reader).Peek(0xc2001e4ba0, 0x1, 0x0, 0x0, 0x0, ...)
 /usr/local/go/src/pkg/bufio/bufio.go:107 +0xc9
net/http.(*persistConn).readLoop(0xc200166180)
 /usr/local/go/src/pkg/net/http/transport.go:670 +0xc4
created by net/http.(*Transport).dialConn
 /usr/local/go/src/pkg/net/http/transport.go:511 +0x574

goroutine 7 [select]:
net/http.(*persistConn).writeLoop(0xc200166180)
 /usr/local/go/src/pkg/net/http/transport.go:774 +0x26f
created by net/http.(*Transport).dialConn
 /usr/local/go/src/pkg/net/http/transport.go:512 +0x58b

goroutine 10 [runnable]:
net.runtime_pollWait(0x7fe61a4d7e60, 0x72, 0x0)
 /usr/local/go/src/pkg/runtime/znetpoll_linux_amd64.c:118 +0x82
net.(*pollDesc).WaitRead(0xc200200e90, 0xb, 0xc20014e3f0)
 /usr/local/go/src/pkg/net/fd_poll_runtime.go:75 +0x31
net.(*netFD).Read(0xc200200e10, 0xc2003c0000, 0x8000, 0x8000, 0x0, ...)
 /usr/local/go/src/pkg/net/fd_unix.go:195 +0x2b3
net.(*conn).Read(0xc200304148, 0xc2003c0000, 0x8000, 0x8000, 0x55622d, ...)
 /usr/local/go/src/pkg/net/net.go:123 +0xc3
crypto/tls.(*block).readFromUntil(0xc200305180, 0xc2003ce240, 0xc200304148, 0x5, 0xc200304148, ...)
 /usr/local/go/src/pkg/crypto/tls/conn.go:401 +0xbd
crypto/tls.(*Conn).readRecord(0xc20016a000, 0x17, 0x0, 0x4215b3)
 /usr/local/go/src/pkg/crypto/tls/conn.go:481 +0xfa
crypto/tls.(*Conn).Read(0xc20016a000, 0xc200305810, 0x24, 0x24, 0x0, ...)
 /usr/local/go/src/pkg/crypto/tls/conn.go:796 +0x102
labix.org/v2/mgo.fill(0xc20030fc60, 0xc20016a000, 0xc200305810, 0x24, 0x24, ...)
 /home/sidnei/src/go/src/labix.org/v2/mgo/socket.go:437 +0x59
labix.org/v2/mgo.(*mongoSocket).readLoop(0xc2003070e0)
 /home/sidnei/src/go/src/labix.org/v2/mgo/socket.go:454 +0x113
created by labix.org/v2/mgo.newSocket
 /home/sidnei/src/go/src/labix.org/v2/mgo/socket.go:156 +0x266

goroutine 11 [sleep]:
time.Sleep(0x2540be400)
 /usr/local/go/src/pkg/runtime/ztime_linux_amd64.c:19 +0x2f
labix.org/v2/mgo.(*mongoServer).pinger(0xc200307000, 0xc200307001)
 /home/sidnei/src/go/src/labix.org/v2/mgo/server.go:270 +0xfd
created by labix.org/v2/mgo.newServer
 /home/sidnei/src/go/src/labix.org/v2/mgo/server.go:80 +0xd9