Many ftp connections into FTP server from Camel route when using recipientList

Issue

We are running a Camel route that produces messages to an FTP server.
At runtime we see hundreds of connections into the FTP server, which do not seem to get cleared up.

Our route in essence looks similar to this example:

<route>
  <from uri="" >
  <!-- some further processing -->
  ...
  <recipientList>
    <simple>
      sftp://server
    </simple>
  </recipientList>
</route>