No windows machines at all on the network, just this debian machine and a mac. It's happening right now with this being the only machine on the subnet.
As for the differing hardware addresses, very observant! I made one of them up just for privacy, just for privacy even though I'm sure it really doesn't matter, and forgot to change the other. In reality there's only one hardware address. By the way, I've noticed the same thing when connecting by wireless.
