wp_rewrite

I’m having the hardest time getting my plugin rewrite rules to work. Here’s my hook:

public function __construct() {
   add_filter('generate_rewrite_rules', array($this, 'createRewriteRules'));
  ...
}
public function createRewriteRules($wp_rewrite) {
	  $tag = 'shop';

    $newrules = array(
                        "{$tag}/(.+?)" => 'index.php?pagename=shopping&q=' . $wp_rewrite->preg_index(1),
                      ); 

    $wp_rewrite->rules =  $wp_rewrite->rules + $newrules;
    return $wp_rewrite;
	}

When I print the wp_rewrite rules right before I return it above, I get:

Array
(
[robots\.txt$] => index.php?robots=1
[.*wp-atom.php$] => index.php?feed=atom
[.*wp-rdf.php$] => index.php?feed=rdf
[.*wp-rss.php$] => index.php?feed=rss
[.*wp-rss2.php$] => index.php?feed=rss2
[.*wp-feed.php$] => index.php?feed=feed
[.*wp-commentsrss2.php$] => index.php?feed=rss2&withcomments=1
[feed/(feed|rdf|rss|rss2|atom)/?$] => index.php?&feed=$matches[1]
[(feed|rdf|rss|rss2|atom)/?$] => index.php?&feed=$matches[1]
[page/?([0-9]{1,})/?$] => index.php?&paged=$matches[1]
[comments/feed/(feed|rdf|rss|rss2|atom)/?$] => index.php?&feed=$matches[1]&withcomments=1
[comments/(feed|rdf|rss|rss2|atom)/?$] => index.php?&feed=$matches[1]&withcomments=1
[comments/page/?([0-9]{1,})/?$] => index.php?&paged=$matches[1]
[search/(.+)/feed/(feed|rdf|rss|rss2|atom)/?$] => index.php?s=$matches[1]&feed=$matches[2]
[search/(.+)/(feed|rdf|rss|rss2|atom)/?$] => index.php?s=$matches[1]&feed=$matches[2]
[search/(.+)/page/?([0-9]{1,})/?$] => index.php?s=$matches[1]&paged=$matches[2]
[search/(.+)/?$] => index.php?s=$matches[1]
[category/(.+?)/feed/(feed|rdf|rss|rss2|atom)/?$] => index.php?category_name=$matches[1]&feed=$matches[2]
[category/(.+?)/(feed|rdf|rss|rss2|atom)/?$] => index.php?category_name=$matches[1]&feed=$matches[2]
[category/(.+?)/page/?([0-9]{1,})/?$] => index.php?category_name=$matches[1]&paged=$matches[2]
[category/(.+?)/?$] => index.php?category_name=$matches[1]
[tag/(.+?)/feed/(feed|rdf|rss|rss2|atom)/?$] => index.php?tag=$matches[1]&feed=$matches[2]
[tag/(.+?)/(feed|rdf|rss|rss2|atom)/?$] => index.php?tag=$matches[1]&feed=$matches[2]
[tag/(.+?)/page/?([0-9]{1,})/?$] => index.php?tag=$matches[1]&paged=$matches[2]
[tag/(.+?)/?$] => index.php?tag=$matches[1]
[author/([^/]+)/feed/(feed|rdf|rss|rss2|atom)/?$] => index.php?author_name=$matches[1]&feed=$matches[2]
[author/([^/]+)/(feed|rdf|rss|rss2|atom)/?$] => index.php?author_name=$matches[1]&feed=$matches[2]
[author/([^/]+)/page/?([0-9]{1,})/?$] => index.php?author_name=$matches[1]&paged=$matches[2]
[author/([^/]+)/?$] => index.php?author_name=$matches[1]
[([0-9]{4})/([0-9]{1,2})/([0-9]{1,2})/feed/(feed|rdf|rss|rss2|atom)/?$] => index.php?year=$matches[1]&monthnum=$matches[2]&day=$matches[3]&feed=$matches[4]
[([0-9]{4})/([0-9]{1,2})/([0-9]{1,2})/(feed|rdf|rss|rss2|atom)/?$] => index.php?year=$matches[1]&monthnum=$matches[2]&day=$matches[3]&feed=$matches[4]
[([0-9]{4})/([0-9]{1,2})/([0-9]{1,2})/page/?([0-9]{1,})/?$] => index.php?year=$matches[1]&monthnum=$matches[2]&day=$matches[3]&paged=$matches[4]
[([0-9]{4})/([0-9]{1,2})/([0-9]{1,2})/?$] => index.php?year=$matches[1]&monthnum=$matches[2]&day=$matches[3]
[([0-9]{4})/([0-9]{1,2})/feed/(feed|rdf|rss|rss2|atom)/?$] => index.php?year=$matches[1]&monthnum=$matches[2]&feed=$matches[3]
[([0-9]{4})/([0-9]{1,2})/(feed|rdf|rss|rss2|atom)/?$] => index.php?year=$matches[1]&monthnum=$matches[2]&feed=$matches[3]
[([0-9]{4})/([0-9]{1,2})/page/?([0-9]{1,})/?$] => index.php?year=$matches[1]&monthnum=$matches[2]&paged=$matches[3]
[([0-9]{4})/([0-9]{1,2})/?$] => index.php?year=$matches[1]&monthnum=$matches[2]
[([0-9]{4})/feed/(feed|rdf|rss|rss2|atom)/?$] => index.php?year=$matches[1]&feed=$matches[2]
[([0-9]{4})/(feed|rdf|rss|rss2|atom)/?$] => index.php?year=$matches[1]&feed=$matches[2]
[([0-9]{4})/page/?([0-9]{1,})/?$] => index.php?year=$matches[1]&paged=$matches[2]
[([0-9]{4})/?$] => index.php?year=$matches[1]
[[0-9]{4}/[0-9]{1,2}/[^/]+/attachment/([^/]+)/?$] => index.php?attachment=$matches[1]
[[0-9]{4}/[0-9]{1,2}/[^/]+/attachment/([^/]+)/trackback/?$] => index.php?attachment=$matches[1]&tb=1
[[0-9]{4}/[0-9]{1,2}/[^/]+/attachment/([^/]+)/feed/(feed|rdf|rss|rss2|atom)/?$] => index.php?attachment=$matches[1]&feed=$matches[2]
[[0-9]{4}/[0-9]{1,2}/[^/]+/attachment/([^/]+)/(feed|rdf|rss|rss2|atom)/?$] => index.php?attachment=$matches[1]&feed=$matches[2]
[[0-9]{4}/[0-9]{1,2}/[^/]+/attachment/([^/]+)/comment-page-([0-9]{1,})/?$] => index.php?attachment=$matches[1]&cpage=$matches[2]
[([0-9]{4})/([0-9]{1,2})/([^/]+)/trackback/?$] => index.php?year=$matches[1]&monthnum=$matches[2]&name=$matches[3]&tb=1
[([0-9]{4})/([0-9]{1,2})/([^/]+)/feed/(feed|rdf|rss|rss2|atom)/?$] => index.php?year=$matches[1]&monthnum=$matches[2]&name=$matches[3]&feed=$matches[4]
[([0-9]{4})/([0-9]{1,2})/([^/]+)/(feed|rdf|rss|rss2|atom)/?$] => index.php?year=$matches[1]&monthnum=$matches[2]&name=$matches[3]&feed=$matches[4]
[([0-9]{4})/([0-9]{1,2})/([^/]+)/page/?([0-9]{1,})/?$] => index.php?year=$matches[1]&monthnum=$matches[2]&name=$matches[3]&paged=$matches[4]
[([0-9]{4})/([0-9]{1,2})/([^/]+)/comment-page-([0-9]{1,})/?$] => index.php?year=$matches[1]&monthnum=$matches[2]&name=$matches[3]&cpage=$matches[4]
[([0-9]{4})/([0-9]{1,2})/([^/]+)(/[0-9]+)?/?$] => index.php?year=$matches[1]&monthnum=$matches[2]&name=$matches[3]&page=$matches[4]
[[0-9]{4}/[0-9]{1,2}/[^/]+/([^/]+)/?$] => index.php?attachment=$matches[1]
[[0-9]{4}/[0-9]{1,2}/[^/]+/([^/]+)/trackback/?$] => index.php?attachment=$matches[1]&tb=1
[[0-9]{4}/[0-9]{1,2}/[^/]+/([^/]+)/feed/(feed|rdf|rss|rss2|atom)/?$] => index.php?attachment=$matches[1]&feed=$matches[2]
[[0-9]{4}/[0-9]{1,2}/[^/]+/([^/]+)/(feed|rdf|rss|rss2|atom)/?$] => index.php?attachment=$matches[1]&feed=$matches[2]
[[0-9]{4}/[0-9]{1,2}/[^/]+/([^/]+)/comment-page-([0-9]{1,})/?$] => index.php?attachment=$matches[1]&cpage=$matches[2]
[([0-9]{4})/([0-9]{1,2})/comment-page-([0-9]{1,})/?$] => index.php?year=$matches[1]&monthnum=$matches[2]&cpage=$matches[3]
[([0-9]{4})/comment-page-([0-9]{1,})/?$] => index.php?year=$matches[1]&cpage=$matches[2]
[.+?/attachment/([^/]+)/?$] => index.php?attachment=$matches[1]
[.+?/attachment/([^/]+)/trackback/?$] => index.php?attachment=$matches[1]&tb=1
[.+?/attachment/([^/]+)/feed/(feed|rdf|rss|rss2|atom)/?$] => index.php?attachment=$matches[1]&feed=$matches[2]
[.+?/attachment/([^/]+)/(feed|rdf|rss|rss2|atom)/?$] => index.php?attachment=$matches[1]&feed=$matches[2]
[.+?/attachment/([^/]+)/comment-page-([0-9]{1,})/?$] => index.php?attachment=$matches[1]&cpage=$matches[2]
[(.+?)/trackback/?$] => index.php?pagename=$matches[1]&tb=1
[(.+?)/feed/(feed|rdf|rss|rss2|atom)/?$] => index.php?pagename=$matches[1]&feed=$matches[2]
[(.+?)/(feed|rdf|rss|rss2|atom)/?$] => index.php?pagename=$matches[1]&feed=$matches[2]
[(.+?)/page/?([0-9]{1,})/?$] => index.php?pagename=$matches[1]&paged=$matches[2]
[(.+?)/comment-page-([0-9]{1,})/?$] => index.php?pagename=$matches[1]&cpage=$matches[2]
[(.+?)(/[0-9]+)?/?$] => index.php?pagename=$matches[1]&page=$matches[2]
[shop/(.+?)] => index.php?pagename=shopping&q=$matches[1]
)

You can see the last element is what I added.

If I visit index.php?pagename=shopping&q=category/1234 everything works fine. though if I visit /shop/category/1234 I get page not found.

Any advice would be much appreciated. Thanks!