The system is fine, you have been playing unrated games recently. For example:
http://www.stooorage.com/show/467/903085_unrated1.jpg
(by clicking the "Details" tab on the game page)
Unrated games can be differentiated by a "u" in front of the time control in the "Challenges" tab.
p.s. I think my "writing with a mouse skills" may be improving. 
anyone knows how to fix it? the rating doesnt change with the game