stack-update adding a parameter leads to heat stack-list breaking

I did a stack-update of a stack that:
 - changed format (to HOT)
 - added a parameter ('Debug')
 - supplied that parameter in the new environment file

and now CFN metadata polling is broken, and heat stack-list errors as well.

In the API log I see:
2014-08-10 23:20:38.890 6176 DEBUG heat.api.middleware.version_negotiation [-] Processing request: GET /v1/43a9170dc5cb47b88ffd40acff0bf0e9/stacks Accept: application/json process_request /opt/stack/venvs/heat/local/lib/python2.7/site-packages/heat/api/middleware/version_negotiation.py:51
2014-08-10 23:20:38.890 6176 DEBUG heat.api.middleware.version_negotiation [-] Matched versioned URI. Version: 1.0 process_request /opt/stack/venvs/heat/local/lib/python2.7/site-packages/heat/api/middleware/version_negotiation.py:66
2014-08-10 23:20:38.891 6176 DEBUG keystoneclient.middleware.auth_token [-] Authenticating user token __call__ /opt/stack/venvs/heat/local/lib/python2.7/site-packages/keystoneclient/middleware/auth_token.py:666
2014-08-10 23:20:38.891 6176 DEBUG keystoneclient.middleware.auth_token [-] Removing headers from request environment: X-Identity-Status,X-Domain-Id,X-Domain-Name,X-Project-Id,X-Project-Name,X-Project-Domain-Id,X-Project-Domain-Name,X-User-Id,X-User-Name,X-User-Domain-Id,X-User-Domain-Name,X-Roles,X-Service-Catalog,X-User,X-Tenant-Id,X-Tenant-Name,X-Tenant,X-
Role _remove_auth_headers /opt/stack/venvs/heat/local/lib/python2.7/site-packages/keystoneclient/middleware/auth_token.py:725
2014-08-10 23:20:38.893 6176 INFO requests.packages.urllib3.connectionpool [-] Starting new HTTP connection (1): 127.0.0.1
2014-08-10 23:20:38.936 6176 DEBUG requests.packages.urllib3.connectionpool [-] "GET /v2.0/tokens/revoked HTTP/1.1" 200 698 _make_request /opt/stack/venvs/heat/local/lib/python2.7/site-packages/requests/packages/urllib3/connectionpool.py:350
2014-08-10 23:20:38.964 6176 DEBUG iso8601.iso8601 [-] Parsed 2014-08-11T03:20:38Z into {'tz_sign': None, 'second_fraction': None, 'hour': u'03', 'daydash': u'11', 'tz_hour': None, 'month': None, 'timezone': u'Z', 'second': u'38', 'tz_minute': None, 'year': u'2014', 'separator': u'T', 'monthdash': u'08', 'day': None, 'minute': u'20'} with default timezone <iso8601.iso8601.Utc object at 0x7f9012c64c90> parse_date /opt/stack/venvs/heat/local/lib/python2.7/site-packages/iso8601/iso8601.py:184
2014-08-10 23:20:38.965 6176 DEBUG iso8601.iso8601 [-] Got u'2014' for 'year' with default None to_int /opt/stack/venvs/heat/local/lib/python2.7/site-packages/iso8601/iso8601.py:140
2014-08-10 23:20:38.966 6176 DEBUG iso8601.iso8601 [-] Got u'08' for 'monthdash' with default 1 to_int /opt/stack/venvs/heat/local/lib/python2.7/site-packages/iso8601/iso8601.py:140
2014-08-10 23:20:38.966 6176 DEBUG iso8601.iso8601 [-] Got 8 for 'month' with default 8 to_int /opt/stack/venvs/heat/local/lib/python2.7/site-packages/iso8601/iso8601.py:140
2014-08-10 23:20:38.966 6176 DEBUG iso8601.iso8601 [-] Got u'11' for 'daydash' with default 1 to_int /opt/stack/venvs/heat/local/lib/python2.7/site-packages/iso8601/iso8601.py:140
2014-08-10 23:20:38.966 6176 DEBUG iso8601.iso8601 [-] Got 11 for 'day' with default 11 to_int /opt/stack/venvs/heat/local/lib/python2.7/site-packages/iso8601/iso8601.py:140
2014-08-10 23:20:38.966 6176 DEBUG iso8601.iso8601 [-] Got u'03' for 'hour' with default None to_int /opt/stack/venvs/heat/local/lib/python2.7/site-packages/iso8601/iso8601.py:140
2014-08-10 23:20:38.966 6176 DEBUG iso8601.iso8601 [-] Got u'20' for 'minute' with default None to_int /opt/stack/venvs/heat/local/lib/python2.7/site-packages/iso8601/iso8601.py:140
2014-08-10 23:20:38.967 6176 DEBUG iso8601.iso8601 [-] Got u'38' for 'second' with default None to_int /opt/stack/venvs/heat/local/lib/python2.7/site-packages/iso8601/iso8601.py:140
2014-08-10 23:20:38.967 6176 DEBUG keystoneclient.middleware.auth_token [-] Storing token in cache _cache_put /opt/stack/venvs/heat/local/lib/python2.7/site-packages/keystoneclient/middleware/auth_token.py:1234
2014-08-10 23:20:38.968 6176 DEBUG keystoneclient.middleware.auth_token [-] Received request from user: de92d8d91cdc4ed79d0819caa7596d3d with project_id : 43a9170dc5cb47b88ffd40acff0bf0e9 and roles: _member_,admin _build_user_headers /opt/stack/venvs/heat/local/lib/python2.7/site-packages/keystoneclient/middleware/auth_token.py:1021
2014-08-10 23:20:38.971 6176 DEBUG heat.openstack.common.policy [req-e0fa3f3f-b3cf-4c67-bdc9-9017e7729603 None] Rules successfully reloaded load_rules /opt/stack/venvs/heat/local/lib/python2.7/site-packages/heat/openstack/common/policy.py:242
2014-08-10 23:20:38.972 6176 DEBUG routes.middleware [req-e0fa3f3f-b3cf-4c67-bdc9-9017e7729603 ] Matched GET /43a9170dc5cb47b88ffd40acff0bf0e9/stacks __call__ /opt/stack/venvs/heat/local/lib/python2.7/site-packages/routes/middleware.py:100
2014-08-10 23:20:38.972 6176 DEBUG routes.middleware [req-e0fa3f3f-b3cf-4c67-bdc9-9017e7729603 ] Route path: '/{tenant_id}/stacks', defaults: {'action': u'index', 'controller': <heat.common.wsgi.Resource object at 0x7f901155a650>} __call__ /opt/stack/venvs/heat/local/lib/python2.7/site-packages/routes/middleware.py:102
2014-08-10 23:20:38.972 6176 DEBUG routes.middleware [req-e0fa3f3f-b3cf-4c67-bdc9-9017e7729603 ] Match dict: {'action': u'index', 'tenant_id': u'43a9170dc5cb47b88ffd40acff0bf0e9', 'controller': <heat.common.wsgi.Resource object at 0x7f901155a650>} __call__ /opt/stack/venvs/heat/local/lib/python2.7/site-packages/routes/middleware.py:103
2014-08-10 23:20:38.973 6176 DEBUG oslo.messaging._drivers.amqpdriver [req-e0fa3f3f-b3cf-4c67-bdc9-9017e7729603 ] MSG_ID is 08c47b6d71ba4d8cadb4519b1d23ce9c _send /opt/stack/venvs/heat/local/lib/python2.7/site-packages/oslo/messaging/_drivers/amqpdriver.py:378
2014-08-10 23:20:38.974 6176 DEBUG oslo.messaging._drivers.amqp [req-e0fa3f3f-b3cf-4c67-bdc9-9017e7729603 ] UNIQUE_ID is 4986dc05f78940c886b2b3e445878f38. _add_unique_id /opt/stack/venvs/heat/local/lib/python2.7/site-packages/oslo/messaging/_drivers/amqp.py:338
2014-08-10 23:20:38.976 6176 DEBUG amqp [req-e0fa3f3f-b3cf-4c67-bdc9-9017e7729603 ] Closed channel #1 _do_close /opt/stack/venvs/heat/local/lib/python2.7/site-packages/amqp/channel.py:104
2014-08-10 23:20:38.976 6176 DEBUG amqp [req-e0fa3f3f-b3cf-4c67-bdc9-9017e7729603 ] using channel_id: 1 __init__ /opt/stack/venvs/heat/local/lib/python2.7/site-packages/amqp/channel.py:80
2014-08-10 23:20:38.977 6176 DEBUG amqp [req-e0fa3f3f-b3cf-4c67-bdc9-9017e7729603 ] Channel open _open_ok /opt/stack/venvs/heat/local/lib/python2.7/site-packages/amqp/channel.py:438
2014-08-10 23:20:39.011 6176 DEBUG heat.common.serializers [req-e0fa3f3f-b3cf-4c67-bdc9-9017e7729603 None] JSON response : {"explanation": "The server could not comply with the request since it is either malformed or otherwise incorrect.", "code": 400, "error": {"message": "The Parameter (Debug) was not defined in template.", "traceback": "Traceback (most recent call last):\n\n File \"/opt/stack/venvs/heat/local/lib/python2.7/site-packages/heat/engine/service.py\", line 63, in wrapped\n return func(self, ctx, *args, **kwargs)\n\n File \"/opt/stack/venvs/heat/local/lib/python2.7/site-packages/heat/engine/service.py\", line 458, in list_stacks\n return [api.format_stack(stack) for stack in stacks]\n\n File \"/opt/stack/venvs/heat/local/lib/python2.7/site-packages/heat/engine/parser.py\", line 233, in load_all\n yield cls._from_db(context, stack, resolve_data=resolve_data)\n\n File \"/opt/stack/venvs/heat/local/lib/python2.7/site-packages/heat/engine/parser.py\", line 250, in _from_db\n use_stored_context=use_stored_context)\n\n File \"/opt/stack/venvs/heat/local/lib/python2.7/site-packages/heat/engine/parser.py\", line 114, in __init__\n context=self.context)\n\n File \"/opt/stack/venvs/heat/local/lib/python2.7/site-packages/heat/engine/parameters.py\", line 437, in validate\n self._validate_user_parameters()\n\n File \"/opt/stack/venvs/heat/local/lib/python2.7/site-packages/heat/engine/parameters.py\", line 480, in _validate_user_parameters\n raise exception.UnknownUserParameter(key=param)\n\nUnknownUserParameter: The Parameter (Debug) was not defined in template.\n", "type": "UnknownUserParameter"}, "title": "Bad Request"} to_json /opt/stack/venvs/heat/local/lib/python2.7/site-packages/heat/common/serializers.py:43