Lifetime memberships created with a start date older than 3 months ago have a status of expired.

When creating a lifetime membership for a contact, if the start date is more than 3 months in the past, the membership status is set as 'Expired'. Clearly a lifetime membership doesn't expire.
I saw this first in a Wordpress install running version 4.4.0, and was repeated by phunter (and myself) on the Drupal 4.4 demo site, which reports as running version 4.4.3.
See the forum thread at http://forum.civicrm.org/index.php/topic,30893.0.html