On my car, if I press unlock and then quickly press lock, the alarm arms itself (in the way the ROW cars do for passive arming) but the doors don't lock. If you open a door, the alarm chirps for about 20 seconds before it goes off. This is different than how my alarm typically operates when the car is locked and a door is manually unlocked (the alarm immediately sounds).

I don't see any benefit of this, and is it a feature or a fault?

 

It's whatever you make of it.