2006 S320 CDI Navigation system restarting issue

[Hillcrest]

I bought a UK 2006 S320 cdi in Auckland, New Zealand. The dealer updated the navigation map with the Navigation DVD Comand Aps 2010 Australia/New Zealand, which is the authorised map. The problem is the navigation system always restarts/reloads repeatly when the destination is in city centre, but it works well while the destination is out of city centre, even from the city centre. Does somebody have any idear about this? Thanks.