published posts not displayed on front end

The most recent posts published on my site are not showing on the front end of my website for some reason. Can you help, please?
When looking at http://fetliu.net/blog/ or http://fetliu.net I don’t see the two latest posts – ‘Setting up a Blackboard Test Course’ and ‘Three Great Things About Xerte’. If you look in the admin you can see they are published, and if you search for them or find them via the tag cloud at the front end, for example, they are visible on the site.

The same problem is happening on the child sites of my network – see http://fetliu.net/babel/ . The latest post that is displayed on the front end, ‘Rejected beauty – Bennita Ciu’, was published on 10 June but three more posts have been published since then that do not appear on the front end of the site.

Is this being caused by Hummingbird Pro, maybe?

Oliver