ews-java-api: StreamingSubscription - Error: Connection is still allocated

For the following code:

        WellKnownFolderName sd = WellKnownFolderName.Inbox;
        FolderId folderId = new FolderId(sd);

        List<FolderId> folder = new ArrayList<FolderId>();
        folder.add(folderId);

        StreamingSubscription subscription = service.subscribeToStreamingNotifications(folder, EventType.NewMail);
        StreamingSubscriptionConnection conn = new StreamingSubscriptionConnection(service, 30);
        conn.addSubscription(subscription);
        EventDelegate delegate = new EventDelegate(service);
        conn.addOnNotificationEvent(delegate);
        conn.addOnDisconnect(delegate);
        conn.open();
        EmailMessage msg = new EmailMessage(service);
        msg.setSubject("Testing Streaming Notification on " + new Date());
        msg.setBody(MessageBody.getMessageBodyFromText("Streaming Notification Test"));
        msg.getToRecipients().add("someone@somewhere.com");
        msg.send();

I get the following error:

 microsoft.exchange.webservices.data.exception.ServiceRequestException: The request failed. Connection is still allocated
 at microsoft.exchange.webservices.data.core.request.SimpleServiceRequestBase.internalExecute(SimpleServiceRequestBase.java:80)
 at microsoft.exchange.webservices.data.core.request.MultiResponseServiceRequest.execute(MultiResponseServiceRequest.java:160)
 at microsoft.exchange.webservices.data.core.ExchangeService.internalCreateItems(ExchangeService.java:592)
 at microsoft.exchange.webservices.data.core.ExchangeService.createItem(ExchangeService.java:651)
 at microsoft.exchange.webservices.data.core.service.item.Item.internalCreate(Item.java:247)
 at microsoft.exchange.webservices.data.core.service.item.EmailMessage.internalSend(EmailMessage.java:147)
 at microsoft.exchange.webservices.data.core.service.item.EmailMessage.send(EmailMessage.java:258)
 at test.TestEWS.main(TestEWS.java:287)
 Caused by: java.lang.IllegalStateException: Connection is still allocated
 at org.apache.http.util.Asserts.check(Asserts.java:34)
 at org.apache.http.impl.conn.BasicHttpClientConnectionManager.getConnection(BasicHttpClientConnectionManager.java:248)
 at org.apache.http.impl.conn.BasicHttpClientConnectionManager$1.get(BasicHttpClientConnectionManager.java:199)
 at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:173)
 at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:195)
 at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:86)
 at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:108)
 at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:184)
 at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:82)
 at microsoft.exchange.webservices.data.core.request.HttpClientWebRequest.executeRequest(HttpClientWebRequest.java:291)
 at microsoft.exchange.webservices.data.core.request.ServiceRequestBase.getEwsHttpWebResponse(ServiceRequestBase.java:780)
 at microsoft.exchange.webservices.data.core.request.ServiceRequestBase.validateAndEmitRequest(ServiceRequestBase.java:719)
 at microsoft.exchange.webservices.data.core.request.SimpleServiceRequestBase.internalExecute(SimpleServiceRequestBase.java:68)
 ... 7 more

I should note that this used to work in the past.

Continuing with some tests on this, creating a separate ExchangeService object for sending the email works. However, the following code still does not work.

        StreamingSubscription subscription = service.subscribeToStreamingNotifications(folder, EventType.NewMail);
        StreamingSubscriptionConnection conn = new StreamingSubscriptionConnection(service, 30);
        conn.addSubscription(subscription);
        conn.open();
        subscription.unsubscribe();
        if (conn.getIsOpen())
            conn.close();

The line subscription.unsubscribe(); will still result in an “Connection is still allocated” error. Also, if I comment it out, the line conn.close(); hangs.