See attached movie and attached application.

There are a list view 100*100 pixels and rectangle 200*200pixels.

I start scrolling using mouse wheel turning over bottom[horizontal] scrollBar. When scrollBar is scrolled on 100% It stops scrolling event consuming and scrolling event starts to come to (I don't know - to list view or to rectangle... Anyway - somewhere else), where that event is catched and scrolling "task" is given to right scrollBar. So, scrolling over horizontal scrollBar I scroll at first horizontal scroll and after that i scroll vertical.