ScrollViewer to scroll freely

I have a stackpanel (stackPanel1) which is inside a scrollviewer.

I have 2 textboxes at the top of stackPane1 then another stackpanel (stackPanel2) which have two buttons, then another stackpanel(stackPanel3) that contains 2 textboxes.

Layout is like so:

scrollViewer
    stackPanel1
            textbox1
            textbox2
            stackPanel2
                    button1
                    button2
            stackPanel3
                    textbox3
                    textbox4

When I scroll through the contents, the scrollviewer "jumps" over stackpanel2 (i.e. when I click the scrollbar, and drag down, it reaches the top of stackpanel2 then "jumps" over button1 and button2 proceedes to the top of stackPanel3 and stops)

But I want the scrollviewer to not "jump" over the contents of stackpanel2. How will I accomplish this without changing the layout?

Thanks.