I edit the sitemaps and upload them to the root folder of my site instead of the cache_html folder. It only takes a minute to take out the images and news index (I use the Google images extension.) Then Google doesn't gripe about my empty sitemap files, and my sitemaps are accepted 100% of the time.
From what I've seen of sitemaps (so far), it's very difficult for any sitemap generator to get it 100% right so Google won't complain. Seems as if it's always something, with Google. So I've found that it's just easier to do a quick cleanup.
And, it's good for me to understand how sitemaps are constructed too. They're easy to edit, they're not very complicated.
That's my two cents, for what it's worth.