The UK and Japan are the only countries in the world that pinpoint destinations to the accuracy of a seven digit postcode, so most of the world's satnav systems find this hard to cope with. The satnav in many German makes has been upgraded with software to try to overcome this, but if the digital mapping has gaps in postcode locations then there will be a problem. It's not the same as not getting seven digit postcode locations at all, it's that the software in your system is not very good at finding them.