When a User creates a new Family Type of a Revit Family the "Key Attribute used for comparing" (used in the Active / Default Item <-> Revit Family Configuration) will be cleared. This will ensure that the new Family Type will not contain a duplicate for the value that is meant to be unique for the dRofus syncing function.
In the following example, "Data: drofus_article_id" is the Revit parameter used as the "Key Attribute for comparing" within the Default Configuration:
This means that if a Revit User were to create a copy of "Type 1" for the Family "Chair-Corbu" by clicking on "Duplicate" when"Type 1" has already been linked to a dRofus Item (using "drofus_article_id" = 6049) (as illustrated below):
..... the new Family Type "Type 2" will have "drofus_article_id" = set to <blank> as shown:
This will ensure that no two or more Family Types (created by the "Duplicate" command) will have the same value as the "Key Attribute used for comparing", meaning the link between the (originally linked) Family Type and the corresponding dRofus Item will never be lost.