title: Git diff working incorrect - to many changes
body: <pre><code>           f1---f2                 - short term branch "feature1"
            /       \
        h--h--h---h--h1--h2-         - long term branch "hofix"
       /       \   \      \
      /         \   \      \
     m----m------m---m------m--      - long term branch "master"
                     |      |
                   1e1e1e 2f2f2f
  </code></pre>
  
  <p>I merge branches with 2 commits difference (15 file changed totaly).
  And ran:</p>
  
  <pre><code>$ git show --pretty="format:" --name-only 1e1e1e..2f2f2f
  </code></pre>
  
  <p>I receive more than 42 000 file changed from my project. Why?</p>
  
  <p>Expected: i will show diff with f1,f2,h1,h2 commits</p>
  
  <p>P.S. May be because "Merge branch 'origin/0411-hotfix'" commit?</p>