I had the same problem last night with a freelander 1 yr 2000.
I found if you unlock the car with the fob, THEN put key fob in your pocket, give it to your partner or take it in the house, you may lock them in car otherwise.
Now open driver and passenger doors, close driver door, walk round to passenger door and lean in then operate the central locking to lock all doors, close the passenger door observe the dash board no flashing alarm light, car is locked but not alarmed.
I further tested this today left the bonnet latched, set alarm opened bonnet and alarm webt off , locked it with central locking switch/passenger door, lifted bonnet no alarm.
I assume if no alarm there is no immobilisation either.