switchClass() removes class if removeClass and addClass params are the same

I am using jQuery 3.6.0. Seems to be an undocumented "feature" with switchClass(). If I specify the same class to remove and then add, I get no class. In the following example, I would expect to see class="big":

   <input type="text" id="myInput" class="big"></input>
   <script>
      $(document).ready(function () {
         $("#myInput").switchClass("big", "big");
      });
   </script>

The above generates:

<input type="text" id="myInput" class="">

Start by reproducing the supplied switchClass("big", "big") example in jQuery UI and trace the switchClass implementation. Done means identical removeClass and addClass parameters no longer leave the element without its class, with a regression test covering the reported behavior.