title: Vim inconsistently syntax highlighting bash files
body: <p>When I open some bash script files with vim it sometimes identifies them as <code>conf</code> files, that's okay, I can just correct that by setting the filetype to <code>sh</code> with <code>:setf sh</code>.</p>
  
  <p>That great, except I've noticed that this doesn't fix things entirely:</p>
  
  <p><img src="https://i.stack.imgur.com/wfAh9.png" alt="Two files side-by-side with different highlighting"></p>
  
  <p>Notice that <code>shopt</code> is properly highlighted on the left, but not on the right, where I manually set the filetype to <code>sh</code>.</p>
  
  <p>This means that when a file is identified as <code>bash</code> or <code>sh</code> by vim, it sets the filetype to <code>sh</code> but then does some extra steps that I'm not doing when I set the filetype manually.</p>
  
  <p>Any one know what that might be, and how I could fix it?</p>