Passenger door wont lock

Hi   new to here , ive just purchased my first skoda , its a bog standard roomster , it has central locking but the old fashioned way use key on lock to open , the problem I am having is I can lock all doors including boot from drivers door apart from the passengers front door , I have to lock that door separately. But if I lock car from passengers side it locks all doors . Is this correct or is there some knack of using this locking system . Thanks