I'm not sure what's there to fix. Source port being random is standart in networking, every application does that.
I don't know much about stunnel, but it appears to make it work on a client, you should connect through port at loopback interface first
application -> 127.0.0.1:selected port -> stunnel client config, mapping selected port to target host:port -> target host:port
And Dmitriy pointed out, $listbuild creates not an instance, but a binary string of special format.
It's a datatype %Library.List, which is one of several datatypes defined, like %Library.Integer or %Library.TimeStamp. Due to implicit conversion these datatypes are often go "invisible" in code, however, it's good to keep in mind what datatypes are you working with.
You can even create your own datatype. Some libraries/frameworks like %ZEN or Ensemble have their own library of datatypes.