I noticed the same thing, and filed an issue [1]. The first reply does not fill me with a lot of confidence (but it's unclear to me whether the person is affiliated with the project or not).
I (partially) fixed this issue, and I'm not affiliated in any way with Signal. It's public (https://github.com/signalapp/Signal-TLS-Proxy/pull/2), and it looks like they welcome contributions, because they merged mine.