Disable Tasks in Chatter Feeds

With Salesforce.com Spring ’13 Release we got the feature: "Chatter feed notification on task creation"and in order to turn it off:

Click Your Name > Setup > Customize > Chatter > Settings and de-select "Tasks in Feed"

Now "Tasks in Feed" checkbox is not there anymore , how can i disable chatter feed notification on task creation?

I have tried:Setup > Customize > Chatter > Feed Tracking, scroll down to Tasks, and disable feed tracking for Tasks but it doesn´t turn off task feeds.

Thanks in advantage for any advice.