Opentok switching between sessions

I am making an application where users can switch between different voice rooms (sessions). The function 'connectToSession' (see below) checks if the user is already in a session, if so will disconnect from current session and then connect to the other session and publish its stream to that session.

The switching of voice rooms works fine and to the user is all apears to be working, however every time a user switches session I get this error in the console:

Publisher State Change Failed:  'Publishing' cannot transition to 'PublishingToSession'
Publisher State Change Failed:  'Publishing' cannot transition to 'Publishing'

From my debugging it seems to have occurred on the line where session.publish is called

var session = null;
var publisher = null;
var subscribers = {};

function connectToSession(sessionId, token) {
    if (session) {
        session.disconnect();
    }

    if (!publisher) {
        //First time so we need to initialise publisher
        var pubOptions = {
            videoSource: null,
            name: user_id
        };

        publisher = OT.initPublisher(null, pubOptions, function() {
            //Publisher initialised
        });

        publisher.on({
            'streamDestroyed': function(event) {
                event.preventDefault();
            }
        });
    }

    session = OT.initSession(apiKey, sessionId);

    session.on({
        'streamCreated': function(event) {
            // Subscribe to others stream
            subscribers[event.stream.name] = session.subscribe(event.stream);
        },
        'sessionConnected': function(sessionConnectEvent) {
            // Session Connected
        },
        'streamDestroyed': function(event) {
            //Stream removed from session
            delete subscribers[event.stream.name];
        }
    });

    session.connect(token,
        function(error) {
            if (error) {
                console.error(error);
            }
            else {
                session.publish(publisher, function() {
                        //Finished publishing
                    }
                );
            }
    });
}

Any ideas what is causing this error?