I would be truly shocked they changed the ability to book mixed-cabin awards. Seriously, shocked. Just HUCA and don't read into it. We would have heard if the policy has in fact changed.
The BOS-HKG issue has to do with the flight is at 1AM so sometimes doesn't quite show up right. I believe the fix it to have the agent specify the time in the search criteria, though I could be remembering incorrectly.