getprotobyname and the default ubuntu:vivid Docker image

Trying to setup a network server on a ubuntu:vivid docker image, I ran into a weird problem - the server would accept the TCP request and then drop the connection. After eliminating a bunch of possible causes (firewall, SELinux), I found that a simple python TCP server I cooked up worked just fine - it was just that particular network server program that was acting up. It worked perfectly fine on the Arch linux distribution running on my laptop though.