The Liberty JMX client starts a background thread to act as a heartbeat, and to poll the server for notifications. The client currently assumes that the heartbeat end point returns no data, when in fact it returns the class name of the JMX server class as a string.
As the input stream containing this data is not read, and the stream is not closed, the underlying socket has to wait for the JVM to eventually perform cleanup. In the meantime, the socket can be left in close wait state.

RESTMBeanServerConnection should fully consume its input streams here: