US citizen with a HK identification card, going from US to HKG. I can enter HK custom using HK ID card (faster line). But when I leave HK, do I use the HKID line, or the foreigner line? If I use the HKID line, I supposed they'll still have to check my US passport? I always wonder if the US Custom will question me re: HK entrance stamps. I don't know if they care that I don't have a "pair" of entrance / exit stamps.

Has anyone done this before?