The car won't lock using the boot lock button

Hi, I've got a Focus Estate Mk2.5 2010 Titanium (I think its a 2.5 because of the new headlight design)

I was wondering if any of you could help me with this weird issue.

So the car has keyless start/stop, and on the front doors I have little back buttons to lock the car.

There is also a button like that on the boot door.

If I press the boot button twice to dead lock the car, it will not dead lock. 

I  can hear the first lock but the second is delayed and the car does not flash its indicators twice to tell me its deadlocked.

Also after that a weird thing happens if I walk off about 10metres and go back to the car, it will start unlocking and locking very quickly by itself. It will sometimes stop after a few seconds but sometimes I have to press unlock on my keyfob a few times to stop it.

The black buttons that are located at the handles at the front doors work fine and deadlock the car with no trouble.

So only the boot button is causing trouble.

Any help would be appreciated thanks.