JQuery function returns incorrect amount of pixels

I have a webview that contains some js and jquery

var viewport_top = $window.scrollTop() is called within a function,

the problem is that this function returns an incorrect amount of pixels, i can see that from displaying an alert

My webview height is around 1600 pixels, when i scroll the height of my screen and call that function, it returns something around 500, which is like +- 1/3rd if what is should be

Why is this happening?