If an item is using defaults then it is using values from the default display. IMPORTANT NOTE: If you modify this value, you are modifying the default display and thus modifying for all displays that are using default values.
If that is not what you intend, you must click the override button. Once overridden, that display now has its own version of the value; modifying it will not modify it for other displays.
For Relationships, arguments, fields, sort criteria, and filters, each of these must be overridden as a group! In other words, you cannot override a single filter, but instead must override all filters. A message will appear on the item to let you know what its status is, but you can only change the status by clicking on the header or the rearrange button for that item.