I see the same behavior when setting up a relation between mysql & keystone.

If I run mysql & keystone on two separate machines, the add-relation works fine.

 If done on the same machine, it fails with the following :

unit-keystone-0: 2014-04-10 09:47:57 ERROR juju.worker.uniter uniter.go:475 hook failed: exit status 1
unit-keystone-0: 2014-04-10 09:55:07 INFO juju-log shared-db:6: db_host or password not set. Peer not ready, exit 0
unit-keystone-0: 2014-04-10 09:55:16 INFO juju-log shared-db:6: Cluster leader, performing db-sync
unit-keystone-0: 2014-04-10 09:55:17 INFO shared-db-relation-changed 2014-04-10 11:55:17.096 10512 CRITICAL keystone [-] (OperationalError) (1
130, "Host '192.168.122.154' is not allowed to connect to this MySQL server") None None
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed Traceback (most recent call last):
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed   File "/var/lib/juju/agents/unit-keystone-0/charm/hooks/shared-db-relati
on-changed", line 570, in <module>
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed     utils.do_hooks(hooks)
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed   File "/var/lib/juju/agents/unit-keystone-0/charm/hooks/lib/utils.py", l
ine 28, in do_hooks
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed     hook_func()
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed   File "/var/lib/juju/agents/unit-keystone-0/charm/hooks/shared-db-relati
on-changed", line 180, in db_changed
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed     ensure_initial_admin(config)
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed   File "/var/lib/juju/agents/unit-keystone-0/charm/hooks/keystone_utils.p
y", line 337, in ensure_initial_admin
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed     create_tenant("admin")
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed   File "/var/lib/juju/agents/unit-keystone-0/charm/hooks/keystone_utils.p
y", line 231, in create_tenant
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed     tenants = [t._info for t in manager.api.tenants.list()]
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed   File "/usr/lib/python2.7/dist-packages/keystoneclient/v2_0/tenants.py",
 line 117, in list
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed     tenant_list = self._list("/tenants%s" % query, "tenants")
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed   File "/usr/lib/python2.7/dist-packages/keystoneclient/base.py", line 90
, in _list
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed     resp, body = self.api.get(url)
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed   File "/usr/lib/python2.7/dist-packages/keystoneclient/httpclient.py", l
ine 654, in get
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed     return self._cs_request(url, 'GET', **kwargs)
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed   File "/usr/lib/python2.7/dist-packages/keystoneclient/httpclient.py", l
ine 650, in _cs_request
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed     **kwargs)
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed   File "/usr/lib/python2.7/dist-packages/keystoneclient/httpclient.py", l
ine 609, in request
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed     **request_kwargs)
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed   File "/usr/lib/python2.7/dist-packages/keystoneclient/httpclient.py", l
ine 114, in request
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed     raise exceptions.from_response(resp)
unit-keystone-0: 2014-04-10 09:55:22 INFO shared-db-relation-changed keystoneclient.exceptions.ClientException: An unexpected error prevented 
the server from fulfilling your request. (OperationalError) (1130, "Host '192.168.122.154' is not allowed to connect to this MySQL server") No
ne None (HTTP 500)
unit-keystone-0: 2014-04-10 09:55:22 ERROR juju.worker.uniter uniter.go:475 hook failed: exit status 1