Is it possible that you registered the day before the 2 week changeover? You obtained 14 activity on your first day (the last day of the 2 week activity period), followed by 14 activity in your second day (the first day of a new 2 week activity period)?
That is exactly what happened, and it was planned by me to see how the system worked. The surprise was that I didn't get the 28 activities in two 14 point hits, but that activity increased shortly after each post during the first couple of days of membership.