When one/a person, adds Mac addresses into the MAC Address list. It works just fine. However when you came back later in a new session with the Router, and add an extra one or more Mac addresses, the firmware deletes all the previously entered addresses and stores only the new ones added in this latest session. Very Irritating.
Suggest that you fix the bug to not overwrite / clear all the existing Mac Addresses, AND/OR allow a long string of Mac addresses to be pasted into the add field, with addresses separated by another delimiter character, like space or '/'. In this way one can maintain a list of valid Mac addresses in a notepad txt file and simply cut and past once.