Android NodeJs socket.emit goes wrong acting like socket.broadcast

Question

I have a problem when using socket.emit from Nodejs because all the Android users are getting the message instead of the one that starts the conversation. Let me explain:

From android I have that code run by a user when he create a new post

socket.emit('post.new', data);

At the Node.js I have

socket.on('post.new', function (data) {
    var post = new Post(data);
    post.save();

    socket.emit('post.new.ack', post);
    socket.broadcast.emit('post.create', post);
});

The snippet socket.emit('post.new.ack', post) is supposed to be received only by the Android user who send post.new event but all the android users get that even. Why ?

Is there something I'm doing wrong ?