diff -u b/core/modules/toolbar/js/views/ToolbarVisualView.js b/core/modules/toolbar/js/views/ToolbarVisualView.js
--- b/core/modules/toolbar/js/views/ToolbarVisualView.js
+++ b/core/modules/toolbar/js/views/ToolbarVisualView.js
@@ -242,7 +242,8 @@
       // Update the orientation of the trays.
 
 
-      // @droplet: Sync Body Classes in real time, not after all scripts execution.
+      // Toggle toolbar's parent classes before other toolbar classes to avoid
+      // potential flicker and re-rendering.
       $('body')
         .toggleClass('toolbar-vertical', (orientation === 'vertical'))
         .toggleClass('toolbar-horizontal', (orientation === 'horizontal'));