Piwik tracks the IP that is given as header in the request. So somehow there are requests sending a local IP in the header. That might be the case if the piwik server is behind a load balancer, a proxy is used or something similar.
Do you have anything set in config for "proxy_client_headers" (General)?

Hi,
My piwik is on standard vps with standard installation, my control panel have reserve proxy (I use VestaCP, another good open source project), but my VPS have only localip (127.0.0.1) and internet ip (181.xx.xx.147), don't have local network (10.x.x.x, 172.x.x.x, etc).

Yet it's possible to reverse proxy be causing the problem? Because the problem only appears sometimes.

Closing issue as "Works for me" as per @sgiehl feedback piwik will always use the specified IPs. If there are requests that don't send proper IPs maybe there's a server misconfiguration?

See also http://piwik.org/faq/how-to-install/faq_98/

Hi guys,

I will get another VPS and transfer my piwik instance to see if problem persists, but I think strange this problem is only in some moments and not in all track.

Thanks again