If you're using HTTPRequest to make requests to a server and receive strange OPTION requests and no answers in the client despite your server receiving the messages ok, maybe your problem is that some new browsers [firefox >3] have a security policy to drop all xmlhttprequest (used in AJAX class) for unauthorized clients.
The solution is simple. change response headers to allow communication with your client.
using web.py, here is an example of server that works: https://gist.github.com/1271118
using Flask, there is an example in the Git repository (examples/misc/flaskexamples/flaskcors), and check out the documentation pyjamaswithpocoo.
I would not make any changes on the client as pyjamas jsonrpc uses XHR for jsonrpc, and therefore, depends on the browser's implementation of XMLHttpRequest.