[xwiki-users] Import and Export XAR will lost tree hierarchy?

Import and Export XAR will lost tree hierarchy? I used to have a multi level tree hierarchy inside my wiki space. But, when I import it, all the pages are flatten as the direct children of the space WebHome. I use the default export tools to export a large 100M+ xar file under Xwiki-6.3 I use "Admin Tools" application to import large xar file under Xwiki-7.3. Is it incompatible with tree hierarchy?