2000 mk4 Astra door buzzer fault?

Hi all,
Having a problem with ignition/door buzzer & deadlocking vehicle. When I take the ignition key out of the ignition barrel with the drivers side door open, door buzzer stays on for around 2-5 seconds & then goes off. If I pull the key out quickly the buzzer usually goes off straight away. If I close the drivers side door whilst buzzer still going off, I am then unable to deadlock car. As presumably ecu still thinks key is in ignition.

I have changed the ignition barrel, ignition switch & door switch, fault still occurring.

Also tried taking buzzer fuse out of fuse box, stops buzzer, but fault still occurring, just can't hear buzzer & still have probs deadlocking car.

If I wait for door buzzer to go off & shut door, keyfob works fine.

Any ideas?

Thanks.