First of all, Mississauga always assesses and approves the eligibility of the sponsor before the application goes to the overseas visa office - no matter where it ultimately ends up - and then they transfer it. It sounds to me like Mississauga simply made a mistake when they sent the application to Buffalo - did you use your address in Canada as your residential address? If so, that's why - they use the residential address as the indicator of which visa office should receive the file and if they made a mistake and didn't pay attention to whether or not you have legal temporary status in Canada (that would make you eligible to be processed through Buffalo) or that you actually requested the application be processed through MC . . . well, then it goes to Buffalo. When Buffalo got it and started to assess it, they realized it didn't belong with them and they transferred it to MC. Your timeline so far would be right on for that scenario - ap submitted in Dec 2009, takes about 38 days for sponsorship approval at CPC-M, another 3 weeks for Buffalo to get the file and start the login process and then they find out they shouldn't have it.
I doubt very much that it has anything at all to do with an interview being required - if you were eligible to have your application processed through Buffalo (either by being a US citizen or permanent resident or by having valid temporary status in Canada) then Buffalo would have kept the file, regardless of whether an interview was required or not. But it's too early for that to have even been determined yet. Buffalo will not have done anything as far as processing - it's obvious that the file was transferred because it wasn't supposed to be in Buffalo in the first place. So, my guess, Mexico City will be processing it entirely. Their posted
processing timeline is 6-15 months from receipt.
