Sometimes feel annoying all twitter posts are re-posted to facebook Wall. The reason behind is You are connected to the Facebook App and given access twitter to post on FB Timeline. For preventing twitter posting on facebook timeline do the following step
1. Take the Profile/Settings menu on Twitter
2. visit the apps tab.
3. Find the Facebook connection and click the Disconnect link.
4. Sign out of both your Twitter and Facebook accounts.
5. Close your browser, clear your cache and cookies(ctrl+H and Clear Browsing Data). Open your browser and sign back int Twitter account.