Mini satnav incorrect postcode data

[Morte]

Hi all. We have a Countryman Cooper SD with built in Satnav. For some reason, it doesn't know where our postcode is, it sends us 6 miles away. If you enter the address by street, it finds it. We've had an identical courtesy car that doesn't have the same problem, pus the latest software update from mini, to no avail. Ours is the only postcode we've had an issue with s far, but we've only tried 4 or 5 others. Has anyone else seen this issue?