When you make a new master page “based on” an existing one, Dorico keeps the text frames in the copy linked to the original, so any edits in them will propagate. Also, within a Master Page the frames on the L and R sides get linked in the same way. This is by design and it’s very useful. But is there a way to break this link in specific cases? Often I want to make variant Master Pages that keep the formatting of their base model but with slightly different headers. Or I want the headers on the L and R to have different content. The only way I can currently see to do this is to delete the frame and recreate it from scratch, but being able to “fork” frames while keeping their formatting would save me quite a lot of time.
My solution (so fr) has been the same as yours: recreate the independent frames from scratch.
As Derrek suggests, the way to break them is to recreate them.
Thought as much. In that case, consider this a humble FR