Random setting not working

I have many SRP widgets on the same page. All but one are using setting to display latest posts. On one widget I’d like to show 1 post randomly from all the posts in the category. The setting Randomly is On, but it doesn’t work. I am always getting the last one. My site
Today it is showing the post ‘The secret of taijiquan’.
Any suggestion, please?

http://ww.wp.xz.cn/plugins/special-recent-posts/