What could make the Jaguar 2000 S-Type exterior loud alarm sound after unlocking the driver door with the key and then immediately opening the door with the driver door handle ?

This sequence should make clear to the car computerthat the owner is opening the door.
I notice this maybe once every 3 times I open the car.

Could some random combination of clockwise and counter-clockwise key turns when the car was originally locked cause this, or someone trying to open the car without the key while it was locked cause this ? Valet button is off.
Couldthe key mechanism bebroken or unconnected in some way ?

 

Haven't had that happen with my 2000 S Type (yet) . . does it do it when using the remote to unlock the door or just the key? Tried using the second key to isolate the problem??[]

 

I have been watching the red light on the surface of the dashboard center, which seems to indicate whether the car alarm is armed or not. Sometimes, when the key is turned anti-clockwise or forward, to unlock the car, sometimes that light does not go out.
I then turn the key back to neutral then repeat the key unlock until that light goes out.
That seems to be a workaround to avoid all the excitement within earshot of the car.
The remote FOB unlock seems to never fail, so the problem seems to be between the lock mechanicals and the electronics of the alarm system.
Similar problem exists for the opening of the trunk.