diff --git a/wp-includes/class-wp-customize-setting.php b/wp-includes/class-wp-customize-setting.php
index 9f72966734..d176d6aa2a 100644
--- a/wp-includes/class-wp-customize-setting.php
+++ b/wp-includes/class-wp-customize-setting.php
@@ -206,6 +206,19 @@ class WP_Customize_Setting {
 		}
 	}
 
+	/**
+	 * Reset `$aggregated_multidimensionals` static variable.
+	 *
+	 * This is intended only for use by unit tests.
+	 *
+	 * @since 4.5.0
+	 * @access public
+	 * @ignore
+	 */
+	static public function reset_aggregated_multidimensionals() {
+		self::$aggregated_multidimensionals = array();
+	}
+
 	/**
 	 * The ID for the current site when the preview() method was called.
 	 *
diff --git a/wp-includes/class-wp-customize-widgets.php b/wp-includes/class-wp-customize-widgets.php
index 0b7b7ceac2..0a73953167 100644
--- a/wp-includes/class-wp-customize-widgets.php
+++ b/wp-includes/class-wp-customize-widgets.php
@@ -99,7 +99,7 @@ final class WP_Customize_Widgets {
 		}
 
 		add_filter( 'customize_dynamic_setting_args',          array( $this, 'filter_customize_dynamic_setting_args' ), 10, 2 );
-		add_action( 'after_setup_theme',                       array( $this, 'register_settings' ) );
+		add_action( 'widgets_init',                            array( $this, 'register_settings' ), 95 );
 		add_action( 'wp_loaded',                               array( $this, 'override_sidebars_widgets_for_theme_switch' ) );
 		add_action( 'customize_controls_init',                 array( $this, 'customize_controls_init' ) );
 		add_action( 'customize_register',                      array( $this, 'schedule_customize_register' ), 1 );
@@ -376,6 +376,8 @@ final class WP_Customize_Widgets {
 	public function customize_register() {
 		global $wp_registered_widgets, $wp_registered_widget_controls, $wp_registered_sidebars;
 
+		add_filter( 'sidebars_widgets', array( $this, 'preview_sidebars_widgets' ), 1 );
+
 		$sidebars_widgets = array_merge(
 			array( 'wp_inactive_widgets' => array() ),
 			array_fill_keys( array_keys( $wp_registered_sidebars ), array() ),
@@ -509,8 +511,6 @@ final class WP_Customize_Widgets {
 				$this->manager->get_setting( $new_setting_id )->preview();
 			}
 		}
-
-		add_filter( 'sidebars_widgets', array( $this, 'preview_sidebars_widgets' ), 1 );
 	}
 
 	/**
diff --git a/wp-includes/version.php b/wp-includes/version.php
index becb457924..2af113e24b 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.5-RC1-37165';
+$wp_version = '4.5-RC1-37166';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.