Renewing non-primary membership results in doubled (or even tripled) expiration time.

When a non-primary membership is renewed, the membership is renewed multiple times in a single instance. If you go through the standard user renewal process and renew once, your expiration date will be doubled or tripled from what it is set in CiviCRM.

For instance, this membership was renewed a single time:
http://drupal.demo.civicrm.org/civicrm/contact/view/membership?action=view&reset=1&cid=210&id=35&context=membership&selectedChild=member

However, instead of getting 2014 as the expiration date which is what was expected (or even 2015 would have been more appropriate), the user is given 2016, which is 3 times what the membership length is (1 year).

How is this happening? How do we fix this?

Thanks!