title: Why does Intellij show 'ghost' changes in a multi-modular git project?
body: <p>I'm working on a multi-module project with each module being contained in a separate git repo.</p>
  
  <p>When I open the <code>Commit Changes</code> dialog in Intellij, alongside changes to <code>java</code> files I've made, I often see supposed changes to other modules which haven't in fact changed.</p>
  
  <p>In the change-tree, underneath these unchanged modules, there will be an item with just the name of the git repository, with no file extension, and a question mark icon signifying that Intellij doesn't recognize the file type.</p>
  
  <p><a href="https://i.stack.imgur.com/BS9bc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/BS9bc.png" alt="Changes with unknown file type"></a></p>
  
  <p>When I click on the item, the in-built diff viewer gives <code>fatal: Not a valid object name</code> followed by a 40 character hex string.</p>
  
  <p><a href="https://i.stack.imgur.com/l5NIz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/l5NIz.png" alt="40 character hex string, no diff view"></a></p>
  
  <p>If I revert the changes on that module, it will reappear immediately.</p>
  
  <p>Is there a reason this happens, and will it cause any problems?</p>