2.1.594 Part 4 Section 2.18.111, ST_VerticalJc (Vertical Alignment Type)

a.   The standard says that both justification is not used if multiple sections are on a page, and does not specify behavior for other alignment values if multiple sections are on a page.

If there are multiple sections on one page and they have different vertical alignment, then Word will ignore the vertical alignment specified and will use the default value of top.