On the demo, once the minimap has been engaged it will not scroll all the way to the top (in webkit / Opera). The issue seems to be that the top of the viewport is always where the mouse pointer is, but at the start the viewport is above the minimap.

The mouseover event of the minimap obviously doesn't extend past itself, so the viewport can never get back up to the top unless the page scrollbar is used.

I've put a border around the minimap to illustrate.

Starting position:

Scrolled to the "top" after activation