Post thumbnail pictures not showing

Hi,

I hope someone can help me with the thumbnail picture problem in the Network theme. I'm running WP 4.1.1 and the latest version of the theme. Front page post links are showing the default thumbnail like they should when there are no featured picture in the post. The problem is the posts with the featured picture which should automaticly be also the thumbnail picture in the theme, in my case they are blank without any thumbnail.

Here is the test site with the Network theme:
http://testi.minityyli.fi/