look at the first look demo for GridView: http://demos.telerik.com/silverlight/#GridView/FirstLook
Scroll at the bottom of the grid view.
Open the details for the last row (Anne).
Scroll down to view the row details.
Click on the Performance chart tab.
Scroll down again until the bottom.
Now click on the scroll bar and move it gently up: as soon as you move up about the height of a row, the grid view flashes, the row details are redrawn and the selected tab is lost, even if the row details are still visible.
This makes working with the row details of the last row very difficult.