ipscan picks up all ip's

Hi
I’m running an ipscan on our LAN adresses it picks up all the addresses even the ones that we are not using all with the same mac address wich is the address of one of our ADSL routers. If I disable the ether connecting to that ADSL everything is fine. Could it be that the ADSL is running proxy-arp or something 'cause its a preconfigured ADSLrouter I got from the ISP. Is there a way to fix this?

I tried scaning any subnet and Ican pickup the whole subnet every address with the mac address of the adsl router

so, disable proxy-arp on the modem =)