When setting the mode to text/palin the editor doesn't remove syntax highlighting

[benbro]

When changing the mode to plain text ('null' or text/palin)
editor.setOption("mode", 'null');
the editor doesn't remove previous syntax highlighting until you refresh it.

To reproduce, open the demo
http://codemirror.net/mode/javascript/index.html
In firebug set the mode to plain text
editor.setOption("mode", "text/plain");
The code still use the javascript mode for the existing text.
Set the editor value and see that it is now using the plain text mode:
editor.refresh();

Thanks