Datagridview滚动/最后一行问题（.Net Winforms）

I have a grid with 7 and half rows visible. I have managed to display the last row fully but the half row space after the last row does not repaint and shows whatever was there previously. Even if I drag another window over my form with the grid and then minimize it, the empty space shows content of the minimized window. I've tried Invalidate() but no luck.I have a grid with 7 and half rows visible. I h