Page1 postbacks to Page2 using button's PostbackUrl property. To check if
there is a postback from page 1 to page 2

on page 2, check if the PreviousPage.IsCrossPagePostBack is true. Also in
this case even though there is a postback to Page 2,

Page1's Page_Load and button click event is called, but while debugging, the
break point in those methods are not hit.

This is probably a bug.