I wonder if you have changed it in the Component in the library and are expecting it to update existing components in the design to reflect that change?
If so, then that is where the confusion has arisen. The Default Reference is exactly that, a default for when components are first added to a design. After that you can call them whatever you want.
If you need to rename some components then you may need to look at the Rename function, but that may turn out to do more than what you want in that it can swap names on all names with a given stem, but not selectively by a particular type of component.