title: Grep behavior on OS X with --only-matching
body: <p>When I run the following:</p>
  
  <pre><code>printf "1234\n1234" | grep -o '^.'
  </code></pre>
  
  <p>I get the following output on OSX 10.10 with zsh 5.0.5:</p>
  
  <pre><code>1
  2
  3
  4
  1
  2
  3
  4
  </code></pre>
  
  <p>Why? I'd expect this output instead:</p>
  
  <pre><code>1
  1
  </code></pre>
  
  <p>Can anyone reproduce this issue? I get the expected output on Ubuntu 14.04.</p>