This may be due to logic similar to that of a classic feature that I
always deemed a bug: troff begins a new page when the current page is
exactly filled, rather than waiting until forced by content that
doesn't fit. If this condition happens at the end of a document, a
spurious blank page results. Worse, if the page header happens to
change just after the exactly filled page, the old heading will be
produced before the new heading is read.