ZSH Agnoster Theme showing machine name

I have a development server hosted on Digital Ocean, using Ubuntu 14.04. I switched my shell to ZSH and decided to go with the **Agnoster** theme. In order to get `user@hostname` to stop showing, I set the `DEFAULT_USER` in my .zshrc file. For some reason on the ubuntu server, that's not working. The hostname still shows, and will not go away. I'm doing the exact same thing on my Mac OSX, and it works fine. Here are some screenshots: ![enter image description here][1] ![enter image description here][2] Anyone know what's going on? I even tried `DEFAULT_USER="$USER@$HOST"` with no luck. If I go back to the default, **Robby Russell** theme, it works just fine. ![enter image description here][3] [1]: https://i.sstatic.net/2Jq5U.png [2]: https://i.sstatic.net/HRgMV.png [3]: https://i.sstatic.net/Q7ERV.png