Not heard of that one before.
The car does auto relock if you unlock the car and dont open a door, after about 60 secs it will relock, if this is enabled, you can disable and enable this function through the car computer, but the car should not relock once the door is opened and certainly not on its own if the key is in the ignition unless its being driven.
But Im talking Gen 2 cars here, yours is a Gen 1 I expect? different ignition system.
Could be with all the rain we've had water/damp has got into the door lock electrics maybe??