Just called the Admissions Office but no one picked up. To share my experience from last year, it appears that HKS was the last school to decide and many were outraged at the delay past their other deadlines. This year though, I think the admissions started out well-intentioned, one of the HKS "Ambassadors" from open house informed me the results would come out late March and as we all know by now, HKS just couldn't pull it through for the Mid-Careers even though the application deadline was moved three months earlier from past years(last year the deadline was March 12).
For me personally, I was waitlisted on May 18 and rejected 3 days later May 21! My personal inference from all this is admissions is pretty much a numbers game, and Harvard having the biggest Mid-Career MPA program of 200 students (100 Edward Mason, 100 from US) they are presently still figuring out from the admitted Mason's what is the exact number, they will then notify the Mason waitlist-reject list and wait a few days AND then inform us, the US applicants (last group of HKS applicants to receive notice).
That being said, it really doesn't help any of us since we can complain and get anxious all we want, but according to the website, HKS notification date is by April 30th. But the good news for us (note: this is from inference again), the applicant pool has swelled again so it is more difficult for admissions to figure out exactly how many from each program will accept based on empirical evidence. So for those of you who have gotten in and soon who will get in, HKS is getting more and more competitive!