Nope, it's still doing it.
The catch is a brand new one, the cable is fine (not seized) and the release handle works normally with no undue stiffness.
The bonnet is adjusted correctly on the corner rubbers and is straight across the front, the pin on the bonnet itself is greased and the spring moves freely up and down.
The pin alignment is perfect, it goes straight into the middle of the catch when you close the bonnet and there's the usual solid "ping" as it engages the latch.
But, drive down the road and five minutes after you set off the bonnet bounces up on to the safety catch.