[Plugin: WordPress SEO by Yoast] Zero images added to NGG tag sitemap

WordPress version: 3.4.1
WordPress SEO version: 1.2.7

I did this: Added tags to all my NextGen galleries

I expected the plugin to do this: include images in http://www.antoniocabral.com.pt/ngg_tag-sitemap.xml

Instead it did this: did not include any images in http://www.antoniocabral.com.pt/ngg_tag-sitemap.xml

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