I also assume that as you didnot insert section breaks deliberately, then
the Headers and Footers in your document are all "linked to previous" and so
working in any part of the document will change all Headers/Footers wher you
have the page number.
For further reading on Sections, see
http://word.mvps.org/faqs/formatting/workwithsectionscontent.htm
which has good information on how to control and use this aspect of Word.
Please come back if this does not answer your problem.
DeanH