Index: src/wp-includes/shortcodes.php
===================================================================
--- src/wp-includes/shortcodes.php	(revision 39267)
+++ src/wp-includes/shortcodes.php	(working copy)
@@ -421,6 +421,23 @@
 		preg_match('%[a-zA-Z0-9]+%', $front, $matches);
 		$elname = $matches[0];
 
+		// Do pre-check to see if any unfiltered_html type attributes.
+		foreach ( $attributes as &$attr ) {
+			$double = strpos( $attr, '"' );
+			$single = strpos( $attr, "'" );
+			if ( false === $double && false === $single ) {
+				continue 2; // Go to next element.
+			}
+			$open = strpos( $attr, '[' );
+			$close = strpos( $attr, ']' );
+			if ( false === $open || false === $close ) {
+				continue; // Go to next attribute.
+			}
+			if ( ( false === $single || $open < $single ) && ( false === $double || $open < $double ) ) {
+				continue 2; // Go to next element.
+			}
+		}
+
 		// Look for shortcodes in each attribute separately.
 		foreach ( $attributes as &$attr ) {
 			$open = strpos( $attr, '[' );
Index: tests/phpunit/tests/shortcode.php
===================================================================
--- tests/phpunit/tests/shortcode.php	(revision 39267)
+++ tests/phpunit/tests/shortcode.php	(working copy)
@@ -4,7 +4,7 @@
  */
 class Tests_Shortcode extends WP_UnitTestCase {
 
-	protected $shortcodes = array( 'test-shortcode-tag', 'footag', 'bartag', 'baztag', 'dumptag', 'hyphen', 'hyphen-foo', 'hyphen-foo-bar', 'url', 'img' );
+	protected $shortcodes = array( 'test-shortcode-tag', 'footag', 'bartag', 'baztag', 'dumptag', 'hyphen', 'hyphen-foo', 'hyphen-foo-bar', 'url', 'img', 'state_inc', 'state_val' );
 
 	function setUp() {
 		parent::setUp();
@@ -88,6 +88,17 @@
 		return $out;
 	}
 
+	protected $state = 0;
+
+	function _shortcode_state_inc( $atts, $content ) {
+		$this->state++;
+		return do_shortcode( $content );
+	}
+
+	function _shortcode_state_val( $atts, $content ) {
+		return $this->state;
+	}
+
 	function test_noatts() {
 		do_shortcode('[test-shortcode-tag /]');
 		$this->assertEquals( '', $this->atts );
@@ -840,4 +851,21 @@
 		);
 		return wp_json_encode( $arr );
 	}
+
+	/**
+	 * @ticket 33134
+	 */
+	function test_nested_left_to_right() {
+		// Now treated as unfiltered.
+		$content = '<a [state_val]>[state_val]</a>';
+		$this->assertEquals( '<a 0>0</a>', do_shortcode( $content ) );
+		$content = '[state_inc]<a [state_val]>[state_val]</a>[/state_inc]';
+		$this->assertEquals( '<a 1>1</a>', do_shortcode( $content ) );
+		// Quoted attributes with dummy workaround (indicates unfiltered_html).
+		$content = '[state_inc]<a dummy href="[state_val]">[state_val]</a>[/state_inc]';
+		$this->assertEquals( '<a dummy href="2">2</a>', do_shortcode( $content ) );
+		// Quoted attributes without workaround leading to current filtered behaviour.
+		$content = '[state_inc]<a href="[state_val]">[state_val]</a>[/state_inc]';
+		$this->assertEquals( '<a href="2">3</a>', do_shortcode( $content ) ); // Note this should have href="3".
+	}
 }