folks, thank you for all the responses. Basically I think our HR doesn't know the rule (I don't know if this is a new rule or not).
Here is my story:
I asked some friends in early 2005 about applying for AP. All of them told me that if I applied for AP, I had to also apply for EAD, because after I came back on AP, my H1B status would be changed. So I applied for AP and EAD.
I went back to China in the past summer, and came back. At the custome of Detroit, I gave the officer both my AP and EAD, but he didn't check my EAD at all. He just gave the EAD back to me.
After I came back, I called my HR. I clearly told them that my H1B was still valid (my H1B would be expired at the end of next year), and I worked based on H1B before I went back to China, and my I-485 was pending. I was told that if I used AP, then my stauts had been changed, so I had to update my I-9 form by using my EAD. So I went to my HR to update my I-9 form, and now my current EAD is going to expire in about 2 months, and I had to apply for another EAD. According to the discussion in this forum, I really didn't have to update my I-9 form. If I didn't do that, I can still keep my H1B status. However, now, it's too late. I had to use EAD because I already updated my I-9 form.
After I checked this forum, I sent email to my HR, and told them that their understanding about using AP is not right. However, they insisited that if I used my AP, I had to update my I-9 form by using my EAD.
I hope my case is helpful for other friends!