Roger,
The behavior of the dual graph is the same since legacy versions (CCSv1.0, if I recall correctly), and I agree it is similar as opening two single time graphs.
CCS saves the arrangement and contents of views when a debug session is terminated, but if I recall correctly the graph view is usually closed between CCS start/restart (I can reproduce that consistently). The times where I saw the graph (and other views) lingering were tied to an imperfect CCS shutdown (crash/lockup, etc.).
The solution to help streamline the graph parameter input is the Export/Import buttons at the bottom of the graph properties.
Regards,
Rafael