Does MAC address filtering work?

Ever since I upgraded to a new Panoramic WiFi modem/router (Technicolor CGM4331), my MAC address filtering has not been working correctly.  Once the whitelist is completed; the filtering option set to Allow; and the router restarted, the whitelist disappears and is completely empty.  Interestingly the filtering appears to work for a little while (a few weeks) before it just stops working.  At this point, I'm guessing that since the whitelist is empty it is now working correctly and filtering all devices.  If I switch the filtering to AllowAll then all my devices can connect to the internet once more.

Has anyone else noticed this odd behavior?  I don't know why the whitelist disappears which is the main issue.  I've tried resetting the router to factory settings but same behavior.  I'm probably going to exchange the router this weekend.  But I'm wondering if it might be a larger issue with MAC filtering and Cox which isn't fixable?

Thanks in advance for your help!