[Plugin: Google XML Sitemaps] Incompatibility with taxonomy.php?

XML Sitemap Generator for WordPress 3.2.4

I’m getting errors every time build the sitemap. In the debug area, this is repeated many, many times over:

Notice: Only variable references should be returned by reference in /wp-includes/taxonomy.php on line 1233

This is the function in question in taxonomy.php:

function &get_object_term_cache($id, $taxonomy) {
	global $object_term_cache, $blog_id;

	if ( isset($object_term_cache[$blog_id][$id][$taxonomy]) )
		return $object_term_cache[$blog_id][$id][$taxonomy];

	if ( isset($object_term_cache[$blog_id][$id]) )
		return array();

	return false;
}

I believe as a result it looks like the category (which is a country name) is being stripped from the sitemap, breaking the links: https://travelogue.travelvice.com/sitemap.xml

https://www.ads-software.com/extend/plugins/google-sitemap-generator/