Curious if you have ever run into this before...
We are using JSitemapPro to build our sitemaps. I have a similar question into them, and I am guessing it is a config issue with their plugin, but just the same I thought I would let you know and ask if you have come across this before.
No worries if the answers are "no" and "no". ;-)
Obviously not a great long-term scenario if our blog content isn't making it to the sitemap.