HttpURLConnection.getResponseCode() returns -1 on second invocation

I seem to be running into a peculiar problem on Android 1.5 when a library I'm using (signpost 1.1-SNAPSHOT), makes two consecutive connections to a remote server. The second connection always fails with a HttpURLConnection.getResponseCode() of -1

Here's a testcase that exposes the problem:

// BROKEN
public void testDefaultOAuthConsumerAndroidBug() throws Exception {
    for (int i = 0; i < 2; ++i) {
        final HttpURLConnection c = (HttpURLConnection) new URL("https://api.tripit.com/oauth/request_token").openConnection();
        final DefaultOAuthConsumer consumer = new DefaultOAuthConsumer(api_key, api_secret, SignatureMethod.HMAC_SHA1);
        consumer.sign(c);                             // This line...
        final InputStream is = c.getInputStream();
        while( is.read() >= 0 ) ;                     // ... in combination with this line causes responseCode -1 for i==1 when using api.tripit.com but not mail.google.com
        assertTrue(c.getResponseCode() > 0);
    }
}

Basically, if I sign the request and then consume the entire input stream, the next request will fail with a resultcode of -1. The failure doesn't seem to happen if I just read one character from the input stream.

Note that this doesn't happen for any url -- just specific urls such as the one above.

Also, if I switch to using HttpClient instead of HttpURLConnection, everything works fine:

// WORKS
public void testCommonsHttpOAuthConsumerAndroidBug() throws Exception {
    for (int i = 0; i < 2; ++i) {
        final HttpGet c = new HttpGet("https://api.tripit.com/oauth/request_token");
        final CommonsHttpOAuthConsumer consumer = new CommonsHttpOAuthConsumer(api_key, api_secret, SignatureMethod.HMAC_SHA1);
        consumer.sign(c);
        final HttpResponse response = new DefaultHttpClient().execute(c);
        final InputStream is = response.getEntity().getContent()