title: How is it possible that a commit got different commit ids?
body: <p>Hello i have 2 branches</p>
  
  <ul>
  <li>master </li>
  <li>feature_xyz</li>
  </ul>
  
  <p>Some how it happens a couple of commits which originated in master branch and also in feature_xyz got different commit ids.</p>
  
  <p>So it is not more possible to find out which commits are really related to the feature.</p>
  
  <p>We dont cherry-pick those commits.</p>
  
  <p>How is it possible that a commit got different commit ids?
  Normaly a commit should have the same id in all branches.</p>
  
  <p>Is there any merge or rebase option that can cause this issue?</p>
  
  <p>Here my try to reproduce</p>
  
  <pre><code>##### simple Test Setup
  git init
  echo "test" &gt; a ; git add a ; git commit -m "master commit 1"
  git checkout -b feature_xyz
  echo "test" &gt; b ; git add b ; git commit -m "feature commit 1"
  git checkout master
  echo "test" &gt; c ; git add c ; git commit -m "master commit 2"
  git checkout feature_xyz
  echo "test" &gt; d ; git add d ; git commit -m "feature commit 2"
  
  ### Test run 1
  git rebase master
  # Validating by    git log master    compare to     git log feature     The commit ids are identical.
  
  
  ##### complex Test Setup
  rm ./* ; rm .git -rf
  git init
  echo "test" &gt; a ; echo "hello" &gt;&gt; a ; echo "World" &gt;&gt; a ; git add a ; git commit -m "master commit 1"
  git checkout -b feature_xyz
  echo "test" &gt; b ; git add b ; git commit -m "feature commit 1"
  git checkout master
  sed -i -e 's/World/wOrlD/g' a ; git add a ; git commit -m "master commit 2"
  git checkout feature_xyz 
  sed -i -e 's/hello/HELL/g' a ; git add a ; git commit -m "feature commit 2"
  ########################
  
  ### Test run 2
  git rebase master
  git mergetool
  git rebase --continue
  # Validating by    git log master    compare to     git log feature     The commit ids are identical.
  
  ### Test run 3
  git merge master
  git mergetool
  git commit
  # Validating by    git log master    compare to     git log feature     The commit ids are identical.
  </code></pre>
  
  <p>In real world the feature branch is ages old an i have no clue how this effect happen.</p>