Now I'm POSITIVE that RapidXML 1.13 doesn't support working around whitespace-only text nodes using the xml:space="preserve" attribute. I located a PATCH for this very issue on SourceForge:
Link to patch for RapidXML 1.13 whitespace-only text node bug
This patch corrects the problem of RapidXML simply never returning/skipping a valid node when it only contained whitespace. It DOES NOT enable use of the xml:space="preserve" attribute. That would be the preferable method of ENABLING the bugfix. Perhaps someone more familiar with the RapidXML project can make that change in the future.