timboreader on "[Plugin: WordPress SEO by Yoast] Plugin seems to disable WP's native "Are you sure?" alert when clicking away fro"

Over the last year, various sites I've added this plugin are having the issue whereby there is no alert for editors who accidentally click away from a post or page they are editing.
The alert that reads "Are you sure? This page is asking you to confirm that you want to leave - data you have entered may not be saved."
I can only find one other report of this online but can't believe I'm the first to discover/report it! Any knowledge of how to fix it?

http://wordpress.org/extend/plugins/wordpress-seo/