title: Git is deleting an ignored file when i switch branches
body: <p>I have one branch (let's call it B) that ignores a certain file, which <em>isn't</em> ignored in some other branches (eg branch A).  When i switch from branch B to branch A, then back to B again, the file has been deleted.</p>
  
  <p>Is this normal?  I can sort of see how it would happen, in the sense that branch B thinks it's not there, and branch A thinks that it is, so when i go back to B it 'tidies it away'.  But it's kind of annoying.</p>
  
  <p>Any suggestions?</p>