The previous design was causing issues. The software needs to be able to distinguish clearly between a material that is untouched from the library and a material that the user has created. For example when you have been working on two projects that both used a material from the library, but you modified it in one of them. So for both technical reasons, and reasons of clarity, we changed this.
I acknowledge that there is an inconvenience. We are planning to add a "duplicate and replace with duplicate" kind of command that will make things easier.