title: github picks up entire commit history
body: <p>I have somehow picked up the entire commit history of the main branch in my latest pull request. My PR contains the message:</p>
  
  <p><code>This pull request is big! We’re only showing the most recent 250 commits.</code></p>
  
  <p>I have a branch that has a LOT of features. This is a working branch used for testing. I have to break up that branch into individual pull requests with each PR as a separate feature so they can be reviewed. There is some crossover with different features so these separate branches aren't going to be functional.</p>
  
  <p>I branch off of <code>master</code> and then do an uncommitted merge with my latest working branch. I pick out the files I want to merge related to that feature. These PRs don't build upon one another. Each will be up-to-date with <code>master</code> but not each other.</p>
  
  <p>What seems to be happening is that the target branch is picking up the entire history of the working branch. How can I keep this from happening? Could a rebase fix this?</p>