Error when adding a buddylist to a group

When I attempt to add a buddy to a group, I get:

warning: Invalid argument supplied for foreach() in /drupal/modules/contrib/buddylist/buddylist.module on line 640.
warning: Invalid argument supplied for foreach() in /drupal/modules/contrib/buddylist/buddylist.module on line 640.

The code is iterating through $form_values here, and expecting each item to be an array of $buddy => array(). This is not the case for e.g. submit and form_id.