title: What does "Mounted from blah" mean for docker push command?
body: <p>I noticed a strange log statement in our build logs, that seems to only show up the first time a particular image is built. I couldn't find any reference to it in Docker literature. I'm interested in knowing what it means.</p>
  
  <pre><code>The push refers to a repository [mycompany.com:5000/blah]
  a35c50f48e25: Preparing
  // more preparing
  0c3170905795: Waiting
  // more waiting
  47a9d8491623: Mounted from foo
  e856ece746ae: Mounted from foo
  f2ec1bba02a6: Mounted from bar
  6407c62d4add: Mounted from foo
  0c3170905795: Mounted from bar
  df64d3292fd6: Mounted from bar
  5ed59af669b0: Pushed
  a35c50f48e25: Pushed
  </code></pre>
  
  <p>What this "Mounted from foo" mean in the above log, and why does it only show up the first time?</p>