When you have set a TextWrapping for a column, consequently the row's height becomes bigger. As the user scrolls to the bottom, it is possible that the last row is not fully visible, its content has been cut.
RadGridView relies on average row calculations to display the visual elements as you scroll down. Since you have enabled TextWrapping on a column, the default row's height is now more than 25 PX. In that case some of the rows may not be calculated accurately.
If you want to avoid this behavior you may force RadGridView to correctly calculate its rows by setting the RowHeight property to a fixed size. This size should be properly set based on the actual row height you have after the text has been wrapped.