title: Page number always show 1 when generating BIRT PDF report
body: <p>Backgroud:
  Use Java + BIRT to generate report.
  Have two methods, 1st is to generate report in viewer and allow user to choose to export it to different format (pdf, xls, word...), 
  2nd is to call BIRT API to generate report file directly to PDF.</p>
  
  <p>All program are in "Layout", no program in "Master Page".
  Have 1 "Data Set". The fields in "Layout" refer to this DS.
  There is Group in "Layout", gropu by one field.
  In "Group Header", I create one cell to use as page number. "Page : pageNumber".</p>
  
  <p>Problem:
  When I use 1st method to generate report, the page could +1. When I use 2nd method, all page number would show as 1.</p>
  
  <p>Question:
  How to make the page number correct in this case?</p>