I see these lines with a distance of 1 second, so there's always a green line (HTTP) and a black line (TCP retransmission) or a grey line (TCP) and a black line (TCP Dup ACK) I'm on Windows 7 SP1 x64. I'm using a Wiresharp capture filter for the TCP port I'm interested in; I'm using a Wireshark display filter for HTTP More @Wikipedia
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