Errors when adding users to documents/discussions with keyboard

- Go to either the Create Document or Create Discussion widget
- Click Change
- Start entering a name in the typeahead
- Use the keyboard to go down and select a user (enter key)

We are brought back to the previous modal screen straight away, the user is not added to the list and JS errors are present in the console.

![screen shot 2014-02-25 at 17 58 42](https://f.cloud.github.com/assets/109850/2260856/7fbd6a0c-9e46-11e3-9992-e2fcdbc07943.png)

![screen shot 2014-02-25 at 17 55 46](https://f.cloud.github.com/assets/109850/2260842/62693d14-9e46-11e3-90d1-ab930d42537c.png)