Wireshark Strangeness

Playing around with Wireshark, looking at the dissected data, and getting some weird results. Evidently the small echo server I wrote (see below) does not create the correct TCP checksum. I thought that this might be an issue when using lo0 (loopback), but the data simply doesn't show up in Wireshark when going to/from the same IP address (in my case, 172.16.0.10). Shows up in netstat:

tcp4       0      0  172.16.0.10.46002      172.16.0.10.55074      ESTABLISHED
tcp4       0      0  172.16.0.10.55074      172.16.0.10.46002      ESTABLISHED
tcp4       0      0  *.46002                *.*                    LISTEN

Not sure what its issue is.

Loopback pcap file available here.

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