Ticket #22856: 22856.6.diff

wp-admin/includes/update-core.php

@@ -728 +728 @@
                 } //end foreach
         }
 
+        // 3.5 -> 3.5+ - an empty twentytwelve directory was created upon upgrade to 3.5 for some users, preventing installation of Twenty Twelve.
+        if ( '3.5' == $old_wp_version ) {
+                if ( is_dir( WP_CONTENT_DIR . '/themes/twentytwelve' ) && ! file_exists( WP_CONTENT_DIR . '/themes/twentytwelve/style.css' )  ) {
+                        $wp_filesystem->delete( $wp_filesystem->wp_themes_dir() . 'twentytwelve/', true );
+                }
+        }
+
         // Handle $result error from the above blocks
         if ( is_wp_error($result) ) {
                 $wp_filesystem->delete($maintenance_file);