Upgrade Form missing/incomplete

Hi

I've got the membership plugin set up just fine but was wondering how upgrades between subscriptions are handled. Looking through the files there seems to be a shortcode [upgradeform] to complement the [accountform] and [renewform] shortcodes but this does nothing save load the respective style sheet. A quick look in the includes folder reveals an empty 'upgrade.form.php'. Is this an errored download or something that is to follow in a later update?

Regards

Mick