Paragraphs spanning page breaks results in 2 paragraphs. This is unfortunately a behaviour by Open Office. When it has a paragraph that continues on the next page it splits it into 2 paragraphs. I can see no way of identifying this case since such page breaks are not in the content.xml file like soft page breaks are.
Go around this problem by adding empty lines until the whole paragraph is pushed to the next page. This empty space will be generated to APT, but APT will se it as empty paragraphs and ignore them. You can also do a soft page break (ctrl + return) to move the whole paragraph to the next page. This page break will however be available in the generated APT document, which the site generation ignores, but the maven-pdf-plugin does not!