Has anybody out there bought one of the CoPilot dash cam, currently being sold by Tesco petrol stations?

I've got 1, but I'm not sure if it's faulty or it's just how it works.
I'm referring to loop recording. From my understanding, once the sd card is full, it should start erasing and recording over the existing data. This doesn't happen for me, I just get sd card full message, and I have to format the card again.
Anybody with one shed any light?