I think a heading is the text you put into the area you open by double-clicking on the top of a page in Word document. “Heading” and “header” mean the same thing. So I should have corrected the post you've answered.

Word seems to “forget” to save the changes when I revise the text in Section 1's header area and remove page number from that place. But it tells me that it did save them. If it saves the changes, what undoes them?