Using from a regular browser, the relative paths start wherever the TW file is located. The tricky part, as you probably know, is how to save the TW file.
I just booted up TD and can verify that the page=xx doesn't work for me either. I suspect that TD has to especially handle the PDF, and in the process the extraneous arguments get scraped off. When running from the browser, there is no special handling and it's all up to the browser and operating system.
Good luck!
-- Mark