diff --git a/wp-includes/version.php b/wp-includes/version.php
index f0607cc88d..565d9e8eed 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-51841';
+$wp_version = '5.9-alpha-51842';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-includes/widgets.php b/wp-includes/widgets.php
index 61caf6af56..1102105c8d 100644
--- a/wp-includes/widgets.php
+++ b/wp-includes/widgets.php
@@ -1255,7 +1255,15 @@ function _wp_sidebars_changed() {
 }
 
 /**
- * Look for "lost" widgets, this has to run at least on each theme change.
+ * Validates and remaps any "orphaned" widgets to wp_inactive_sidgets sidebar, and saves the widget settings.
+ * This has to run at least on each theme change.
+ *
+ * For example, let's say theme A has a "footer" sidebar, and theme B doesn't have one.
+ * After switching from theme A to theme B, all the widgets previously assigned to the footer would be inaccessible.
+ * This function detects this scenario, and moves all the widgets previously assigned to the footer under wp_inactive_widgets.
+ *
+ * Despite the word "retrieve" in the name, this function actually updates the database and the global $sidebars_widgets.
+ * For that reason it should not be run from the front end unless the param value is 'customize' (to bypass the database write).
  *
  * @since 2.8.0
  *
@@ -1310,6 +1318,7 @@ function retrieve_widgets( $theme_changed = false ) {
 	$sidebars_widgets['wp_inactive_widgets'] = array_merge( $lost_widgets, (array) $sidebars_widgets['wp_inactive_widgets'] );
 
 	if ( 'customize' !== $theme_changed ) {
+		// Update the widgets settings in the database.
 		wp_set_sidebars_widgets( $sidebars_widgets );
 	}