title: Github "Squash and Merge" - subsequent pull request showing all previous changes
body: <p>I have a branch which I pulled from master branch. Let's call it integration. </p>
  
  <p>In the integration branch, I made various commits (C1, C2, C3). When I am done, I made a Pull Request to the master branch. From the master branch, I did a "Squash and Merge" so it results in only a single commit in the master. This all seems great.</p>
  
  <p>But then later, I made some additional changes to the integration branch and when I make a pull request again, I am seeing all the commit comments of previous changes (C1, C2, C3, C4) that I have already committed. This issue is not seen if I use the default "Create an Merge commit" in my earlier commit. What did I do wrong?</p>