Definitely not normal behavour for your unit. From memory, the only time a locked map will work in a particular unit without the necessary gma/unl files is if they have been present and operating alongside an 'official' map originally, but they then are removed in mass storage mode. If the unit is not hard reset afterwards it will continue to read the map normally, but will not recognise it after a hard reset/clear NV memory. I think that's correct and there is no other way a unit can recognise a locked map without those original files corresponding to the unit.