This can be reproduced as follow steps:

1)nova show gcb_test_222
+--------------------------------------+----------------------------------------------------------+
| Property                             | Value                                                    |
+--------------------------------------+----------------------------------------------------------+
| status                               | ACTIVE                                                   |
| updated                              | 2013-09-21T03:45:52Z                                     |
| OS-EXT-STS:task_state                | None                                                     |
| OS-EXT-SRV-ATTR:host                 | kvm-installer-222                                        |
| key_name                             | None                                                     |
| image                                | cirros-Image (c2fdf54f-4978-4ee9-af0e-d1e0d5db2631)      |
| hostId                               | b605c007b2a5de389a65a645d88d708b82745b4706361d9ef18bf410 |
| OS-EXT-STS:vm_state                  | active                                                   |
| OS-EXT-SRV-ATTR:instance_name        | instance-00000038                                        |
| OS-SRV-USG:launched_at               | 2013-09-20T22:45:53.555626                               |
| OS-EXT-SRV-ATTR:hypervisor_hostname  | kvm-installer-222                                        |
| flavor                               | m1.tiny (1)                                              |
| id                                   | 7677f07e-f5f4-42ee-a5d1-f1dbcddab769                     |
| security_groups                      | [{u'name': u'default'}]                                  |
| OS-SRV-USG:terminated_at             | None                                                     |
| user_id                              | d02e0752613142da90387adcc7cf2664                         |
| name                                 | gcb_test_222                                             |
| created                              | 2013-09-21T03:45:49Z                                     |
| tenant_id                            | 6db20e01ef6f42f18cbebb56f70ebed3                         |
| OS-DCF:diskConfig                    | MANUAL                                                   |
| metadata                             | {}                                                       |
| os-extended-volumes:volumes_attached | []                                                       |
| accessIPv4                           |                                                          |
| accessIPv6                           |                                                          |
| net1 network                         | 10.0.2.7                                                 |
| progress                             | 0                                                        |
| OS-EXT-STS:power_state               | 1                                                        |
| OS-EXT-AZ:availability_zone          | nova                                                     |
| config_drive                         |                                                          |
+--------------------------------------+----------------------------------------------------------+
2)nova availability-zone-list
+---------------------------------+----------------------------------------+
| Name                            | Status                                 |
+---------------------------------+----------------------------------------+
| internal                        | available                              |
| |- vapp-0823-kvm-controller-226 |                                        |
| | |- nova-cert                  | enabled :-) 2013-09-21T03:49:11.078833 |
| | |- nova-conductor             | enabled :-) 2013-09-21T03:49:10.851063 |
| | |- nova-consoleauth           | enabled :-) 2013-09-21T03:49:10.693941 |
| | |- nova-scheduler             | enabled :-) 2013-09-21T03:49:10.844385 |
| | |- nova-console               | enabled :-) 2013-09-21T03:49:11.431072 |
| | |- nova-cells                 | enabled :-) 2013-09-21T03:49:11.945337 |
| nova                            | available                              |
| |- kvm-installer-221            |                                        |
| | |- nova-compute               | enabled :-) 2013-09-21T03:49:08.087701 |
| |- kvm-installer-222            |                                        |
| | |- nova-compute               | enabled XXX 2013-09-21T03:47:32.943466 |
+---------------------------------+----------------------------------------+
3)nova stop  gcb_test_222
4)nova show gcb_test_222
+--------------------------------------+----------------------------------------------------------+
| Property                             | Value                                                    |
+--------------------------------------+----------------------------------------------------------+
| status                               | ACTIVE                                                   |
| updated                              | 2013-09-21T03:51:10Z                                     |
| OS-EXT-STS:task_state                | powering-off                                             |
| OS-EXT-SRV-ATTR:host                 | kvm-installer-222                                        |
| key_name                             | None                                                     |
| image                                | cirros-Image (c2fdf54f-4978-4ee9-af0e-d1e0d5db2631)      |
| hostId                               | b605c007b2a5de389a65a645d88d708b82745b4706361d9ef18bf410 |
| OS-EXT-STS:vm_state                  | active                                                   |
| OS-EXT-SRV-ATTR:instance_name        | instance-00000038                                        |
| OS-SRV-USG:launched_at               | 2013-09-20T22:45:53.555626                               |
| OS-EXT-SRV-ATTR:hypervisor_hostname  | kvm-installer-222                                        |
| flavor                               | m1.tiny (1)                                              |
| id                                   | 7677f07e-f5f4-42ee-a5d1-f1dbcddab769                     |
| security_groups                      | [{u'name': u'default'}]                                  |
| OS-SRV-USG:terminated_at             | None                                                     |
| user_id                              | d02e0752613142da90387adcc7cf2664                         |
| name                                 | gcb_test_222                                             |
| created                              | 2013-09-21T03:45:49Z                                     |
| tenant_id                            | 6db20e01ef6f42f18cbebb56f70ebed3                         |
| OS-DCF:diskConfig                    | MANUAL                                                   |
| metadata                             | {}                                                       |
| os-extended-volumes:volumes_attached | []                                                       |
| accessIPv4                           |                                                          |
| accessIPv6                           |                                                          |
| net1 network                         | 10.0.2.7                                                 |
| progress                             | 0                                                        |
| OS-EXT-STS:power_state               | 1                                                        |
| OS-EXT-AZ:availability_zone          | nova                                                     |
| config_drive                         |                                                          |
+--------------------------------------+----------------------------------------------------------+
5)nova stop gcb_test_222
ERROR: Instance 7677f07e-f5f4-42ee-a5d1-f1dbcddab769 in task_state powering-off. Cannot stop while the instance is in this state. 
(HTTP 400) (Request-ID: req-a51eb10b-c034-4ff0-afa5-3e996b812b75)