This can happen if two processes is trying to control the mouse pointer at the same time. If some process want the mouse pointer to be a donut one want it to be a pointer. Normally the program in focus/hover decides/control the pointer, but programs that hook them self into Windows can sometimes control the pointer even if another program should be in control.
I have never seen this my self and never been able to recreate it, So it is impossible for me to say why this happening and what process collides with MC.