Module Views automatically replace underscores in css classname to hyphens?
It's by design... Views module is cleaning class in views_plugin_style.inc..

  /**
   * Return the token replaced row class for the specified row.
   */
  function get_row_class($row_index) {
    if ($this-&gt;uses_row_class()) {
      $class = $this-&gt;options['row_class'];
      if ($this-&gt;uses_fields() &amp;&amp; $this-&gt;view-&gt;field) {
        $class = strip_tags($this-&gt;tokenize_value($class, $row_index));
      }

      $classes = explode(' ', $class);
      foreach ($classes as &amp;$class) {
        $class = drupal_clean_css_identifier($class);
      }
      return implode(' ', $classes);
    }
  }


Below statement is converting _ (Underscore) to - (hyphens)

$class = drupal_clean_css_identifier($class);


If you see documentation of drupal_clean_css_identifier by default filters replaces _ with -.