1) Maybe not post a bug yet, wait until other users come up with this problem. Probably writer: 'json' works if you send data from the model. Bugs you can post on the Bug thread.
2) You're right it is not anymore in the documentation, but people left some comments about it in the API.
3) People mark their own answers all the time. Mark the post you think is the best answer to the problem you posted. If this is marked people will know it is solved, so mark something.