This is a question about the scrolling function of the datagrid. When the user clicks on the area between the scrollthumb and scrollarrow, the grid scroll to the row that was the last in view when it first loaded, that is the first visible row is the 10th row now(given the fact that the grid can display 10 rows at a time). Similarly all subsequent single clicks on that area scroll up the grid by 9. However once the user keeps the mouse button pressed at this location for a while before releasing this behavior is altered. All mouse clicks henceforth scroll the grid to multiples of 9 rather than 9.