Just thought I'd share this if someone else encounters the same problems I did trying to use this class.
The documentation for the .NET HttpListener class states that a Prefix host name + is similar to * without going into any further details.
There is actually a pretty big difference between the two.
There is also no mention of what happens when you specify an IP addresses as the host name (weak wildcard).
The full explanation is found in the MSDN documentation for the "HTTP Server API" under "UrlPrefix Strings".