Magic Mouse stops scrolling

Just got a new iMac with magic mouse. Often, in the middle of a page, the mouse stops responding to gestures and I have to resort to using the scroll bar. Why? Is the mouse defective?

When it stops scrolling, can you lift your fingers, tap and then continue to scroll? I've found that sometimes I'm on some "sleep" threshold or something...it'll be scrolling and then I'll stop for a moment to read something and when I try to scroll, nothing happens, but just a tap (not click) on top gets me going again.

If yours doesn't get going immediately and you need to do something more than that, it might be defective..

Regards