title: Wordpress seems to replace all underscores with dashes since 9.1.2 in uploaded files. How can I remove this?
body: <p>I have noticed that it seems like that Wordpress is replacing all underscores with dashes in uploaded file names since the lastest update (9.1.2). However, I need the underscores in the file names to be kept.</p>
  
  <p>I found a plugin that I modified but it doesn't seem to help.. See the code below.</p>
  
  <pre><code>function mfl_make_filename_lowercase($filename) {
      $info = pathinfo($filename);
      $ext  = empty($info['extension']) ? '' : '.' . $info['extension'];
      $name = basename($filename, $ext);
      $name = preg_replace('/-/', '_', $name);
      return strtolower($name) . $ext;
  }
  add_filter('sanitize_file_name', 'mfl_make_filename_lowercase', 10);
  </code></pre>
  
  <p>I have looked around quite a bit, I have checked the formatting.php in wp-includes and changed the preg_replace to '_' instead of '-' where I found it. I have done the same in files.php in wp-admin/includes. </p>
  
  <p>I must be missing something. Or is it simply not possible? Please help!</p>