ADDITIONAL SYSTEM INFORMATION :
It happens also on linux (originally discovered in QA environment), but I am able to reproduce on a mac.

A DESCRIPTION OF THE PROBLEM :
This bug is VERY similar to JDK-8221395, except that this bug only happens with HTTP/2 protocol using a proxy tunnel. The JDK-8221395 test case only fixes the HTTP/1 case, so I modified it to use HTTP/2 to reproduce this issue.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. git clone https://github.com/tinyproxy/tinyproxy.git # clone tinyproxy repo
2. cd tinyproxy # go into tinyproxy checkout
3. ./autogen.sh && ./configure && make # build tinyproxy
4. src/tinyproxy -d -c etc/tinyproxy.conf # start tinyproxy server, it will listen on port 8888
5. java SocketSandbox.java # start socket server (repro)
6. telnet localhost 59090

Wait a few minutes, for the connection to time out. You'll see tinyproxy terminate the connection to nghttp2.org, but netstat will show a leaked TUNNEL to the proxy in CLOSE_WAIT state, it will look something like this.

tcp4      24      0  127.0.0.1.58252        127.0.0.1.8888         CLOSE_WAIT 

This will never get close()'d.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The socket connection to the proxy should eventually be closed.
ACTUAL -
The socket connection to the proxy remains in CLOSE_WAIT indefinitely until the java process ends. There is always some small amount of bytes (e.g. 24) in Recv-Q.

---------- BEGIN SOURCE ----------
import java.io.PrintWriter;
import java.net.InetSocketAddress;
import java.net.ProxySelector;
import java.net.ServerSocket;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpClient.Version;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.net.http.HttpResponse.BodyHandlers;

public class SocketSandbox {
  public static void main(String[] args) throws Exception {
    try (var listener = new ServerSocket(59090)) {
      System.out.println("Server is running...");
      while (true) {
        try (var socket = listener.accept()) {
          HttpClient client = HttpClient.newBuilder()
                                        .version(Version.HTTP_2)
                                        .proxy(ProxySelector.of(new InetSocketAddress("127.0.0.1", 8888)))
                                        .build();
          HttpRequest request = HttpRequest.newBuilder(URI.create("https://nghttp2.org/httpbin/anything")).build();
          HttpResponse<String> response = client.send(request, BodyHandlers.ofString());
          var out = new PrintWriter(socket.getOutputStream(), true);
          out.println(String.format("Response HTTP status: %s", response.statusCode()));
        }
      }
    }
  }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
This issue can be worked around by explicitly disabling the http/2 protocol via Version.HTTP_1_1. The bug does not happen at all, except with HTTP/2, and only when a proxy is used.

FREQUENCY : always