Shortcode breaks Shadowbox

The following shortcode function to pull content from another post breaks Shadowbox’s ability to apply the rel attribute to the appropriate links. I’m guessing apply_filters is overriding SB plugin functionality but I’m not sure. Suggestions?

function digwp_includeContentShortcode( $atts ) {
          $thepostid = (int) $atts['postidparam'];

          if ( ! $post = get_post( $thepostid ) )
               return '<em>Invalid post/page ID.</em>';

          return apply_filters( 'the_content', $post->post_content );
}
add_shortcode("digwp_include", "digwp_includeContentShortcode");

http://ww.wp.xz.cn/extend/plugins/shadowbox-js/