Hello
I got the same problem, "Close" put my websocket client in infinite loop.
Server receives the "Close" message from the client but does not actually send the response, because it is in non-blocking mode.
I just do this change in uppsrc/core/WebSocket.cpp , function "out":

// while(IsBlocking()  && socket->IsOpen() && !IsError() && out_queue.GetCount())
   while((IsBlocking() || (s[0] == CLOSE))  && socket->IsOpen() && !IsError() && out_queue.GetCount())

and got "Close" working well...

void WebSocket::Out(const String& s)
{
	out_queue.AddTail(s);
	while((IsBlocking() || close_sent) && socket->IsOpen() && !IsError() && out_queue.GetCount())
		Output();
}