PushCommand throws JSchException: UnknownHostKey

Question

I'm using JGit to call a push command without using StrictHostKeyChecking set to NO, but I get the following error:

UnknownHostKey: <server hostname>. RSA key fingerprint is: <...>

The SSH key is set on the server, the known_hosts file contains the server hostname. I can do a push from the command line, but not from code.

Here's my code:

SshSessionFactory sshSessionFactory = new JschConfigSessionFactory()
    {
        @Override
        protected void configure(final OpenSshConfig.Host hc, Session session) 
        {
            session.setPassword(passphrase);
        }

        @Override
        protected JSch createDefaultJSch(FS fs) throws JSchException
        {
            JSch jsch = super.createDefaultJSch(fs);
            jsch.removeAllIdentity();
            jsch.addIdentity("path to id_rsa");
            jsch.setKnownHosts("path to known_hosts");
            return jsch;
        }

    };

    //SshSessionFactory.setInstance(sshSessionFactory);

    TransportConfigCallback tcc = new TransportConfigCallback()
    {
        @Override
        public void configure(Transport transport) 
        {
            SshTransport sshTransport = (SshTransport) transport;
            sshTransport.setSshSessionFactory(sshSessionFactory);
        }
    };

    pushCommand.setTransportConfigCallback(tcc);
    pushCommand.setPushTags().call();