I resolved the issue by changing the "join" form box (on the splash page) to "login" form box. This stopped the "leave the page?" message. So I changed the code:

   <div class="bx-spl-cell bx-spl-c2 bx-hide-when-logged-in">

              <div class="bx-spl-ccnt bx-def-padding">__join_form_in_box__</div>

            </div>

        </div>

to:

   <div class="bx-spl-cell bx-spl-c2 bx-hide-when-logged-in">

              <div class="bx-spl-ccnt bx-def-padding">__login_form_in_box__</div>

            </div>

        </div>

that fixed it.