title: why the ManipulationDelta in the WP7.1 didn't work very well?
body: <p>As the title says, when upgrade to the Windows Phone 7.1 It seems the ManipulationDelta do not fire as frequency as the version of Windows Phone 7. </p>
  
  <p>eg:
    I have a ScrollViewer, and there are some controls in it. I set the ScrollViewer's ManipulationMode is Control. When i Vertical scrolling, the ManipulationDelta event didn't fire at all. ThereMore, when I Horizontal scrolling,the ManipulationDelta event fired. I don't kown why this happed. How can I use  ManipulationDelta event in the ScrollViewer.</p>