I know you said that you where out of status when you did AOS. Did you file the following forms when you submitted your I-485 packet:
I-566 Interagency Record of Request -- A, G or NATO Dependent Employment Authorization or Change/Adjustment to/from A, G or NATO Status
I-508 Waiver of Rights, Privileges, Exemptions and Immunities (Under Section 247(b) of the INA) (or I-508F if you are French citizen)
The reason that I am asking, is maybe in their system it said that you where still on an A-2 status since the State Department never updated them, and according to the instructions for the I-485, if you are on an A, G, or NATO you can not file unless you filed the I-566 and I-508 (or I-508F) with the I-485.
My wife's non-immigrant status when she applied for AOS was active on a G-4 (Employee of an International Organization). When I was reviewing the forms before filling them out, I noticed the instructions about the I-566 and I-508. So, when I pulled the I-566 and it asked for a Department of State Personal Identification Number (PID). I asked my wife if she had a PID and she didn't know, so she asked the visa office at her organization. They informed her at the time she originally started they weren't applying for PID for employees at her level. However, I called USCIS and asked about filling the forms with no PID and they replied that it is necessary and it would be rejected without it. So, my wife contacted her visa office who informed her it would take up to six weeks to get the number from DOS.
When we went to our interview, the officer looked at some cheat sheet that she had posted and said, "Since you are on a G-4 visa you need an I-508 and I-566 which I already saw in the file." Sounded like according to her comment and what I was told by an USCIS call center agent, they couldn't make a decision on the I-485 if the I-566 and I-508 where missing.
However, if this is the case that you are missing these two forms you would think USCIS would of spotted it earlier and sent you an RFE.