In the last update (2.0.3), a label was added to the search form input for screen readers. It is still missing one attribute to make it pass WCAG 2.0 Level A conformance tests. The input field needs a ID attribute in addition to a name attribute. I added a id=’s’ in a child theme that allow the form to pass.
Here is the full line from my child functions.php:
<input id="s" type="search" placeholder="<?php _e( 'SEARCH', 'parabola' ); ?>" name="s" class="s" value="<?php echo get_search_query(); ?>" />