Wireshark · Wireshark-dev: [Wireshark-dev] Can't capture traffic on some ports

[S <activeco@xxxxxxxxxxx>]

I setup reverse proxy (Pound) to listen on standard ports 80 and 443 and
pipe the data to backend server on the same machine (same IP address),
to ports 81 & 83 respectively.
Although everything passes OK, I can't capture any traffic on ports 81
or 83 either by using tcpdump or wireshark. Capturing data on 80 or 443
goes without problems.
Any help here?