The problem: You have an AS3 Flash movie embedded in a page. You are using mousewheel events inside your Flash (for zooming, scrolling, etc), but don't want the browser window to scroll at the same time, while the mouse is over the Flash (just like AS2).

The solution:

import com.spikything.utils.MouseWheelTrap;
MouseWheelTrap.setup(stage);

...and you're done.