Subject: Dual system brakes...
I'm replacing all of the brake pipes on the Rapide in Cunifer pipework and I realised that the duel system (as setup on the Rapide) has no safety benefit if one system looses pressure...
The brake pedal is connected to the two master cylinders with a bar which is pivoted in the middle (see photo below; taken a while ago) . If one system looses pressure the bar pivots and therefore does not allow you to operate the good side effectively - the pedal hits the floor.
I found this to be the case when I bled one system and tried the brakes.
Just an observation!