Duplicate MAC but different IP? Is this normal? [closed]

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http://serverfault.com – I asked this previously but I have a question. Would it be possible to have duplicate mac but different ip on home router? My questions are listed below. I dont have computers with same MAC. The second connection displays no computer name. Computer Name, Mac, IP David 11:22:33:44:55 11:22:33:44:55 1) Is this normal event? 2) Am I being hacked(aka arp spoofing of some sort?) 3) What causes it? Can this happen time to time and disappear? 4) If I used VPN of some sort, can this cause this problem? I have WPA 2 enabled with mac filtering. (HowTos)