title: Why do I have the same commits in two branches with different hashes
body: <p>I'm a bit puzzled by this...</p>
  
  <p>I have two branches that have the same series of commits in both of them.</p>
  
  <p>The true history is that they were authored by my colleague, committed and pushed to github on branch A. At some stage I merged branch A with my B branch.</p>
  
  <p>What git now appears to show is his commits in branch A, with their hashes, and the same commits in my (diverged) branch, showing me as author, and a different set of hashes, intermingled with the work I was doing on my branch.</p>
  
  <p>This feels like some sort of rebase issue, (we both use GitHubForWindows some of the time which does rebase as part of sync) but I'm not aware of an issue being reported to either of us.</p>
  
  <p>Any ideas on what caused this, or how to get it straight would be appreciated. </p>