This happens in CS2 as well with the offline "help center" windows. I'm really not sure why this happens, but I noticed it far more in XP than in vista or 7.
You can also load the 16bit normal map in to TB2 directly, just be sure to save as PSD as 16 bit tiffs are not supported (they will only load as 8bit).
Thanks for the info. I've had TB2 for a few days but haven't played in it yet. Good to know about how to treat the metals. Looking forward to whatever is next :)