It seems that when you have an animation sequence playing and the application is in windows mode and you move the mouse outside the window or to the window bar at the top, the animations speed up noticeably then change again when you move the mouse back into the window area.

It has nothing to do with fps or how many objects or any thing like that. I just make an animated active object, set its slow and fast speeds to the same, and set the application to windows mode, set fps 100.

Why is this?