Just dont try and touch the screen until the page has completely loaded ! That works fine for me .
Actually the reason for that is becoz when the browser is loading some page , it utilizes ram and so it sometimes becomes unresponsive and doesn't accurately follow your touch.....& so here you go till the bottom of the page , that's really annoying for me also , but i use Opera much more than the default one . You might be wondering the reason for why the opera doesn't take the window till the bottom of the screen , well this is becoz of the flash support , both of them supports flash but opera cannot play the flv's on the window itself while you can watch the other screen contents (Opera does this only in the full screen mode) but in the other browser , (Web app does this in the small screen as well as full screen mode)its better or we could just say newer rather than better coz it makes it a hevy browser !! And that's what makes it take more ram and more processing..
After all , we all agree with demential as he said " maybe it will be fixed in the next software update
I too wish for the same