We recently noticed a bug in the GET action of action_stream.json and contacts.json endpoints.
These endpoints were displaying a next action inside the contact object, which was incorrect and not as documented.
We will be updating so that the api properly matches the documentation here - http://developer.onepagecrm.com/#actionstream
A GET to action_stream.json will return actions by default. The default value of the fields parameter for this request is fields=all,next_actions(all),next_action(all).
You can still change the value to whatever suits your needs however by adding a ?fields= parameter.
You can return action details with a call to contacts.json by adding fields=next_action(all) or fields=next_actions(all)
Please get in touch if you have any questions.