Running Civi 5.8.2 under Drupal 7.63. The title says it all, really. Joint annual members converted to Joint Life during their membership period. This was entered as a renewal with "change membership type", and although the primary Member's End Date was set to Null, the End Date of the Member by relationship remained as before, the end of their annual membership. Fixed quite simply by editing the database record, but seems to be a fault.
Any ideas welcome. Tom Crawshaw