Unregistering service results in ValueError when application stops

[JCorson]

I am getting a ValueError when stopping my application after unregistering a service provided by a ServiceOffer in another plugin.

After some digging, it looks like the CorePlugin._service_ids contains a list of service IDs that were provided to the 'envisage.service_offers' extension point. Then when the plugin stops, it attempts to unregister those services. However, if one of those services was unregistered with Application.unregister_service(<id>), the id is not also removed from CorePlugin._service_ids and stopping the plugin results in the following:

  File "/Users/jcorson/.edm/envs/foo/lib/python3.6/site-packages/envisage/application.py", line 338, in stop
    self.plugin_manager.stop()
  File "/Users/jcorson/.edm/envs/foo/lib/python3.6/site-packages/envisage/composite_plugin_manager.py", line 167, in stop
    self.stop_plugin(plugin)
  File "/Users/jcorson/.edm/envs/foo/lib/python3.6/site-packages/envisage/composite_plugin_manager.py", line 177, in stop_plugin
    plugin.activator.stop_plugin(plugin)
  File "/Users/jcorson/.edm/envs/foo/lib/python3.6/site-packages/envisage/plugin_activator.py", line 49, in stop_plugin
    plugin.unregister_services()
  File "/Users/jcorson/.edm/envs/foo/lib/python3.6/site-packages/envisage/plugin.py", line 285, in unregister_services
    for service_id in service_ids:
  File "/Users/jcorson/.edm/envs/foo/lib/python3.6/site-packages/envisage/application.py", line 422, in unregister_service
    self.service_registry.unregister_service(service_id)
  File "/Users/jcorson/.edm/envs/foo/lib/python3.6/site-packages/envisage/service_registry.py", line 191, in unregister_service
    raise ValueError('no service with id <%d>' % service_id)
ValueError: no service with id <13>