I created a simple plunk that demonstrates the issue.
When I use
angular.injector(['ng', 'MyModule']).get('MyService')
I seem to get a new instance every time it is called, or at least behaves as such. In the plunk, notice how the "Increment" button calls the same instance of the service, as opposed to how the "Call Via Injector" works.
I have been banging my head for hours, tried various things, and read many apparently-relevant posts but to no avail. Any help is appreciated.