Do you have any other protocols besides TCP/IP installed/enabled on systems where you expirience the duplicates? Packet duplication is related to protocol-miniport bindings (an example, when you run Wireshark you have one extra binding for winpcap protocol driver) and loopback packets indications (each outgoing packet from one protocol driver is indicated to every other bound protocol, each incoming packet is indicated to every installed protocol). I think in some cases a sort of mess up is possible especially if you use bridging drivers (which is actually protocol driver which works as packet repeater). If you uninstall WinpkFilter it is fully removed from the stack and plays no role in packet processing. So probaly duplicates caused by some other network components installed on your computer.