I would try clearing your cache. I'm not exactly sure if that will help at all. I'll ask around the office o see if i can come up with a better explanation that hasn't already been mentioned.
Just keep trying to rate it. Or play the game for a little while before you actually rate it. I have had a problem were I tried to rate a game and it didn't do it. But after about 1 minute it showed up.
Below th game there is a box with Game Stats. There is a bar with the game rating, where is written "average" and below is written "your vote". Click with your mouse in a number in the bar to rate the game.
I am having problems with game ratings too. I played Sushi Cat 2 and rated it but when I played it in other moment it was not rated. I cleared my cache and it doesn't work yet.
