title: Git commit lost after merge
body: <p>We have 3 branches (A, B, C) as below:</p>
  
  <pre><code>---\--A1--\------Am------Merge1---An---Merge2---
      \      \              /             /
       \      \--C1---C2---/             /
        \                               /
         \--B1--------------Bn---------/
  </code></pre>
  
  <p>The problem appears at Merge2. Some commit on branch C ( <strong>not all but some</strong>, let's say C2) is lost on branch A after Merge2, which is present between Merge1 and Merge2.</p>
  
  <p>When doing Merge2, there is only one file conflict, which not relates to the lost commit (C2). And we resolve the confilict and finish the merge successfully.</p>
  
  <p><strong>It seems like C2 is reversed by Merge2 on branch A, without any log.</strong></p>
  
  <p>What happened? What might be the cause to this situation?</p>