getting Error on emitWithAck() in v2 beta

[Myotis0815]

When using emitWithAck() in the v2.0.0 beta (combined with v3.0.4 Server on node.js) I get an Error 'invalid payload' from the parser (client code below). I implement a workaround so the parsing itself does work for my case now, but I still do not get any data in my ack-function.
Using v0.9.x with Server v2.4 I do not have any issues.

Are there any changes in the usage of emitWithAck() from v0.9 to v2.0.

Client Code:
socket.emitWithAck( 'eventName', 'someData', ack: (data) { print(data); } );