title: Attempting to start git bisect gives 'fatal: invalid reference:...'
body: <p>Attempting to start a bisect with the following command,</p>
  
  <pre><code>git bisect start
  </code></pre>
  
  <p>causes Git to respond:</p>
  
  <pre><code>fatal: invalid reference: atrium-3018
  </code></pre>
  
  <p>What is the cause of this and how can I fix it?</p>