When stopping FTP server, thread is blocked forever

The behavior we experience here is that our main thread is stuck forever on the stop action of the FTP server, here's a JConsole output on the stack trace :

rg.apache.ftpserver.listener.nio.NioListener.stop(NioListener.java:204)
org.apache.ftpserver.impl.DefaultFtpServer.stop(DefaultFtpServer.java:118)
***
***
java.util.concurrent.FutureTask.run(Unknown Source)
java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
java.lang.Thread.run(Unknown Source)