Until and including Microsoft Office 2010, Word enabled you to retain the Spacing before value in a paragraph style that included a Page break before, typically Heading 1. This enabled you to start a chapter, for example, part way down a page, which is how it is presented in many publications. The only requirement was to go to File > Options > Advanced > Layout Options and select Don’t use HTML paragraph autospacing.
In Word 2013, this option was removed, meaning all chapters except the first now start at the top of a page.
The easiest way around this limitation is to save the .docx document as .doc.