WebSocket, skips parse_variables at times, why?

I'm currently implementing the Engine.IO (and possibly Socket.IO) protocol in Pike (bidirectional realtime communication with JavaScript clients).

While doing so I noticed (to my dismay) that in WebSocket, I find the following code snippet:

protected int parse_variables() { if (has_index(request_headers, "sec-websocket-key")) return 0; return ::parse_variables(); }

I.e. parse_variables() is skipped on real websocket connections. What would be the reason why this is being skipped? I need to parse the variables on the URL of the soon-to-be-upgraded websocket connection; so it would be more convenient if it was handled automatically.