DirectX Mouse

After i have created the mouse pointer for directx, something happens to the
tracking of the mouse pointer.
i create:
sprintf(buffer,"Pointer (%d,%d)",mouse_x,mouse_y);
and i realised that the pointer loses its position if i move it quickly.
Lets say the original position is (320,240), after i move my mouse left and
right a few times and when back at the initial position, the figures change.
How does this happen? What can i do to solve this problem?