We have discovered a small issue with QNetworkInterface. The QNetworkInterface::IsPointToPoint flag is not correctly set on winXP and above. Win2K is fine because it uses a separate function. In qnetworkinterface_win.cpp, we have two ways of querying the system for MACs, interfaceListingWinXP() and interfaceListingWin2K(). Whereas the win2k version correctly sets QNetworkInterface::IsPointToPoint, guess what, the winXP version never sets it at all!
I can confirm that the win32 IP_ADAPTER_ADDRESSES struct has the correct IfType = IF_TYPE_PPP (23) for a PPP link but Qt never uses it to set the QNetworkInterface::IsPointToPoint flag.
Here's the MSDN about it: http://msdn.microsoft.com/en-us/library/aa366058%28v=VS.85%29.aspx
This is a very easy fix, so I have attached a patch for you.