It only seems that Word removes the top and bottom margins. If you click that icon, Word hides the white space at the top and bottom of the page. When you move the mouse pointer to the top or bottom edge of the page, Word changes the mouse pointer to a small icon with two arrows pointing toward each other (up and down). You won't know why the margins are gone or how to get them back. It's a helpful feature if you need it, but if you don't know it exists when your margins suddenly disappear, you might feel a bit lost.
Word lets you hide the white space (including the headers and footers) at the top and bottom of a page, thereby fitting more content on the screen. This isn't a phantom gremlin it's actually an obscure feature that's a bit too easy to engage.
Sometimes, the top and bottom margins seem to disappear. In Print Layout view, Word displays a 'sheet of paper.' Each onscreen border represents the edge of a single sheet.
