Shifted doc which is fixed entering and exiting the header

[Paguro Bernardo]

I've got a word document (generated via OLE starting froma DOT) with
this strange behavior:
When I open it in Word, all the lines are shifted down just if there
was an extra line at the beginning.
If I just double click on the header (which is completely empty) and
then close it, everything goes back to its right position.

Is there someone who can explain me what can be happening?

Thanks a lot,
Francesco.