One other idea for you, WordPress.com has technically been on WordPress 4.3 for a bit, even though WordPress 4.3 was just released today (think of them as the world's largest test bed).
I don't see any changes made in 4.3 to the export/import system, but try upgrading your self-hosted installation to 4.3 to see if that makes any difference. It's worth a shot while waiting for answers from the WordPress.com end.
