回複：And, at what port did u return to US? buffalo?

1. I filed I-485 and I-131 on July 2
2. Went to Canada and returned to US on Aug 31 (AP still pending at that time, but received 485 receipt)
3. AP approved on Sep. 28
4. I went and return by Land through Surrey, WA

At least for my case, my AP application was still valid even after I went abroad. As I said, the officers did not ask anything about I-485.