> So it looks like -me and -ms break the .sp request in this context. Well "break" is probably not the right word, since it implies that this behavior is "not correct", whereas the behavior is actually intended. The macro packages set up a top margin and skip this margin when outputting text. Additionally, they might set the "no space" flag, to disable vertical space from being output at the top of the page (e.g., you might want a small space between paragraphs, but not before a paragraph that begins on a new page).
I think that the vertical position is initialized to -1 before any text has been output is also by design, to be able to set page margins on the first page with a ".wh 0 xx" trap. To quote the Troff User's Manual: A pseudo-page transition onto the first page occurs either when the first break occurs or when the first nondiverted text processing occurs. Arrangements for a trap to occur at the top of the first page must be completed before this transition.
