I've seen this happen in other applications as well, overshooting the active window area your mouse cursor while sizing an object or area causes the window positioning to accelerate.
Yet the speed at which the window position moves is directly related to the amount by which your mouse cursor overshoots the active area border edge.
For example, with the cursor touching the inner edge, the window position moves very slowly, as you move your cursor further out of the area the speed increases.
This is also related to Mouse sensitivity, which can be adjusted in Windows control.