A parent information is dynamically added to a document link when producing the XHTML when the document does not exist. The problem is that XHTML parser expect the query string in the href to be the source one and does not know that parent parameter is dynamically generated.
The result is that when you have a page containing
edit with the WYSIWYG and then save, it becomes
The solution is to save everything Link object is containing in the XHTML marker to not loose it.