title: Incorrect "Can't rebase immutable changeset" error
body: <p>Occasionally, when I do a pull with rebase, I get the following error:</p>
  
  <pre><code>abort: can't rebase immutable changeset fa044e766d1f
  hint: see hg help phases for details
  </code></pre>
  
  <p>Funny thing is, that changeset that errors (and it is the same one every time) is very old, and is already public.</p>
  
  <p>Here's a screenshot:<a href="https://db.tt/xHiOxm6R" rel="nofollow">https://db.tt/xHiOxm6R</a></p>
  
  <p>It appears that I can just ignore the message (at least, so far, I've not gotten into any trouble by doing so), but obviously, I'd like to help Hg resolve this issue so that its not going to continue to be a hassle in the future.</p>
  
  <p>Thanks.</p>
  
  <h2>Update</h2>
  
  <p>hg out does not list it.  The clone is probably about 6 months old.  Also, as far as I know, none of the other developers are experiencing this problem.</p>