Scroll bar problem in PrintPreview control

I have a customized Print Preview dialog made of a Print Preview control.
When I increase to zoom property, the document inside it gets enlarged and two scroll bars appear. But when I scroll down with Vertical scroll bar, it doesn't go till the bottom and bounce back upwords if I resize(enlarge) the Dialog it self. It doesn't show the bottom of the document in any case.
More over when the dialog is compressed and the document in side the preview control is not 100 % visible widthwise, the expected horizontal scroll doesn't appear.
What is the reason for such behavior? :ehh:
Please guide