Michel,
What do you mean by 'locking mode"? If the key opened the boot, it is 'unlocked'.
If the car is in 'Valet Mode', the boot switch on the fascia will not function to open the boot. Trying to use the switch should show 'Valet Mode' on the instruments. There are two ways to cancel Valet Mode. One is to lock and unlock the car with the Remote Fob. The second is to open the boot with a master key, which you have done. The signal to cancel Valet Mode is the two boot interior lights coming on. If for some reason those lights do not come on, the Valet Mode will fail to cancel. If that's the case, that will have to be investigated.
Cheers,