masterpage in BIRT report with RTC

Hello everybody,
     I wish to have a header page with a dynamic variable. I watch this video:
https://www.youtube.com/watch?v=lw_k1qHY_gU

It's work in the preview mode but after deploying the report in RTC, the behaviour is different.
When I set my pageVariable on "onPageBreak" method, My pageVariable used in the masterpage is updating only for the next page.
Example:
I have a workitem per page and I want to have the number of the workitem in the header of the page:
page1:
    - header with number WI n°1
    - body with information of the WI n°1
page 2:
    - header with number WI n°2
    - body with information of the WI n°2
...
...
Unfortunately I have:
page 1:
      - header: nothing
      - body with information of the WI n°1
page 2:
       - header with number WI n°1
       - body with information of the WI n°2
...
..
The information between header and body of the page is shifting.
Does anyone have a workaround about it ?

thank

Best regards