fixes #6473

IPython/html/static/notebook/js/celltoolbar.js

@@ -254,6 +254,7 b' var IPython = (function (IPython) {'
         // which is probably inner_element
         // or this.element.
         this.inner_element.empty();
+        this.show();
 
         var callbacks = CellToolbar._callback_dict;
         var preset = CellToolbar._ui_controls_list;