Coherent top offset usage

I'm seeing some trouble when saving the element's (<form> one in my case) *top offset* before fixing and then applying the same value as its *top CSS attribute* when unfixing. Maybe I'm missing something but I can't figure out why you'd want to do that?

The problem I experienced was that when my element was unfixed, it got position:relative and top:xxx, which made it jump down a lot and essentially become invisible to the user. This fix takes care of that.