When i am using LUNA to navigate and speedcams are detected, the camera and distance spoken are okay, but, the speedlimit sound is incorrect.

It always says the limit is only about 60% of the true value. e.g. The actual limit is 30 mph and the spoken limit is 19 mph, the actual limit is 40 mph and the spoken limit is 25 mph.

Is this a known fault or have i got something wrong.