Bug in the scheduled update of Membership Statuses?
A real fix is still needed but the following procedure appears to provide a reliable workaround:


Set the Grace period to the new value; 
Disable the status 'Expired';  
Run the task 'Update Membership Statuses' so that memberships within the new Grace period are set to 'Grace'; (but don't just run Cron, as Cron only runs this particular update task once a day.) 
Re-enable the status 'Expired';  
Run the update task a second time to check that memberships that really should have expired do indeed correctly show as 'Expired'. 


David