title: Squashing a release branch to master results in duplicate history on each subsequent release
body: <p>I'm using a Github release strategy that works in the following way:</p>
  
  <ul>
  <li>Checkout a release branch from develop using <code>git checkout -b release-x.x.0 develop</code></li>
  <li>Update <code>package.json</code> to match release branch version</li>
  <li>Squash and merge release branch to master and develop</li>
  </ul>
  
  <p>Each release branch contains a series of squashed commits from pull requests. Master has its own hotfixes that are merged separately into develop.</p>
  
  <p>On subsequent releases, I've noticed that commits on master continue to appear multiple times after the merge. For example:</p>
  
  <ul>
  <li>Merge squashed PRs #1-3 into develop</li>
  <li>Create a release branch from develop to merge #1-3 into master with a squashed commit for "Release 1.1.0"</li>
  <li>Merge squash PRs #4-6 into develop</li>
  <li>Create a release branch from develop merging #4-6 into master with a squashed commit for "Release 1.2.0"</li>
  <li><strong>When comparing this second release branch, history for PRs #1-6 is displayed instead of only #4-6</strong></li>
  </ul>
  
  <p>Is this the expected behavior resulting from squashing the release?</p>
  
  <p>If so, I'm assuming that switching my release strategy to normal merging the branch to master will resolve it going forward, but what's the best way to get the history of master to match develop for now?</p>