Posted by seneca (441 days ago)
My experience: I have repeatedly had an expired passport containing a current visa (Mainland resident's permit) plus a new passport with zero stamps and visas. The old passport would be perforated as a sign that it has expired; the visa, however, will be valid until you get a new one. I had to carry both my passports - the old one to prove I had a visa, the new passport for the Immigration official to place his chops.
This seems to be international practice. You will therefore not need to transfer your old HK Immigration stamp to your new passport until you get a new HK visa.
Then again, it's somewhat cumbersome travelling on two passports...
(I am based in Hong Kong)