Wp-cli import not importing modified pages

I am using wp-cli to export and import pages in WordPress 4.0. When I just modify the content of page and then do an export and import into another WP instance, the import process does not import that modified page and says page already exists. Do you know what is the criteria to import a modified page. In the xml generated by export, I do not see the latest page modification date which would probably the best criteria to determine if the page has changed.