It appears that this plugin is using SimpleHttpConnectionManager incorrectly, according to our Jenkins log:

The following message appears (nearly) every minute in our Jenkins log:

Feb 2, 2014 7:42:50 AM org.apache.commons.httpclient.SimpleHttpConnectionManager getConnectionWithTimeout
WARNING: SimpleHttpConnectionManager being used incorrectly. Be sure that HttpMethod.releaseConnection() is always called and that only one thread and/or method is using this connection manager at a time.

Since it has no prefix, I can't be sure this is indeed GHPRB but since this is the only thing that runs that often I assume it is.