Styling hides all checkboxes but doesn't replace all with icons

[zosnap]

There's this style rule defined in the buttons module (line 244 of _buttons.scss)

  // Hide radio buttons and checkboxes within button groups
  input[type=checkbox], input[type=radio] {
    position: absolute;
    left: -9999em;
  }

This hides all checkboxes and radio buttons. It's accompanied by a whole set of other style rules that replace standard checkboxes and radio buttons with icomoon icons and style the label elements to look like buttons. However, these rules are only applied to checkboxes accompanied by labels with the class "btn". This results in checkboxes that aren't accompanied by "btn" labels being hidden but not replaced with anything.

You can see the issue in lines 135-242 of _buttons.scss.