An issue with Windows Phone's built-in Twitter feature has been confirmed by Microsoft to be using excessive data...
Source: http://www.phonearena.com/news/Windows-Phones-built-in-Twitter-client-racking-up-massive-data-usage-a-fix-is-already-live_id48709
Source: http://www.phonearena.com/news/Windows-Phones-built-in-Twitter-client-racking-up-massive-data-usage-a-fix-is-already-live_id48709