OP
It means that if a person receives an electric shock the RCD will disconnect fast enough to prevent them dying, but the solar PV will continue to output voltage for up to 5 seconds, more than long enough to kill them and char-grill the body.
Not good. Thing is though, if the Solar PV is on it's own circuit protected by it's MCB and/or additional protection from a RCD then disconnection ( from mains) will occur within 40mS for earth leakage or 400mS on earth fault or short circuit.
But as you say, the solar PV will continue output for up to 5 seconds feeding the live conductors leaving the inverter and earth path fault via person or metallic object.
And because the protective earth conductor is connected to the MET then all exposed and extraneous parts will be live for that duration until the generator shutdown.
Surely the inverter should shutdown within 400mS as is the regulation for all final circuits under 32A.