Why does Jetty JSR356 behave differently with regards to checkOrigin and modifyHandshake

I was playing around with Jetty (9.2.3v20140905) by connecting a web socket endpoint where I tried to use my own ServerEndpointConfig when I came across Jetty's code to see how it was used. I notice that it is used in JsrCreator when a web socket object is created:

Object createWebSocket(ServletUpgradeRequest req, ServletUpgradeResponse resp){
 ...
 // modify handshake
 configurator.modifyHandshake(config,hsreq,hsresp);
 ...
}

I read the javadoc of modifyHandshake of ServerEndpointConfig (javax.websocket-api 1.0) that states:

Called by the container after it has formulated a handshake response resulting from a well-formed handshake request. The container has already checked that this configuration has a matching URI, determined the validity of the origin using the checkOrigin method, and filled out the negotiated subprotocols and extensions based on this configuration. Custom configurations may override this method in order to inspect the request parameters and modify the handshake response that the server has formulated. and the URI checking also. If the developer does not override this method, no further modification of the request and response are made by the implementation.

Here's what Jetty does:

Object createWebSocket(ServletUpgradeRequest req, ServletUpgradeResponse resp){
 ...
 // modify handshake
 configurator.modifyHandshake(config,hsreq,hsresp);

 // check origin
 if (!configurator.checkOrigin(req.getOrigin())){...}
 ...
 resp.setAcceptedSubProtocol(subprotocol);
 ...
 resp.setExtensions(configs);
}

As you can see, the origin is checked after the configurator as been called. The response is modified after the configurator as been called. The method acceptWebSocket of WebSocketServerFactory makes a call to the WebSocketCreator:

Object websocketPojo = creator.createWebSocket(sockreq, sockresp);

And after that calls:

private boolean upgrade(HttpConnection http, ServletUpgradeRequest request, ServletUpgradeResponse response, EventDriver driver)

which also modifies the response via HandshakeRFC6455:

 // build response
 response.setHeader("Upgrade","WebSocket");
 response.addHeader("Connection","Upgrade");
 response.addHeader("Sec-WebSocket-Accept",AcceptHash.hashKey(key));

So I have no way modifying the response only with my configurator because Jetty will change it anyway.

It seems to me Jetty does not comply with JSR 356, the Java API for WebSocket, does it?