Geo IP mistake (no replies)

Hi guys! Recently is noticed that my Piwik does not dectect the real location of the visitors. I tried with a VPN located in Singapore and it detected the IP in UK! Then I tried again with a VPN in Brasin, and now for it i was in USA. So, I can see only visitors form USA or UK, could be some mistake in the code? Or that is correct?

Thanks,
Peter