Ticket #20534: 20534.diff

wp-admin/includes/post.php

@@ -1155 +1155 @@
                         $thumbnail_html = wp_get_attachment_image( $thumbnail_id, array( $content_width, $content_width ) );
                 else
                         $thumbnail_html = wp_get_attachment_image( $thumbnail_id, 'post-thumbnail' );
+                if ( force_ssl_admin() ) {
+                        $thumbnail_html = str_replace('http://', 'https://', $thumbnail_html);
+                }
                 if ( !empty( $thumbnail_html ) ) {
                         $ajax_nonce = wp_create_nonce( "set_post_thumbnail-$post_id" );
                         $content = sprintf($set_thumbnail_link, $thumbnail_html);