Your case is somewhat unique. Supposedly, even you are not a US citizen or green card holder, but at some point that if you resided in US legally and continuously over 12 months, and is still living in US (legally or not), the CIC may keep your application being fully processed by CPC-Mississauga at their discretion. Your case was CIC transferred your application to LDVO, which is among the slowest VO to process applications, and I think whoever did the initial review found that you were qualified to be processed as a US applicant, and thus, they transferred your application back to US local VO at their choice to reduce their work loads. Although comparing to CPC-Mississauga, LAVO is a bit slower, but if your case is straight forward, it shouldn't take long. Actually, the person who decided to transfer your application back to US DID you a huge favor, in the means of reducing your processing time.
Now, to all other US applicants that their applications to be transferred from CPC-Mississauga to US local VOs, it is because there might have some issues in the application that required a further assessment. And to those applicants, their processing time is longer than usual.