Apparently Blizz stealth-nerfed the formula for calculating Arena points in 2.1. Blizz only admitted it when someone confronted them in the General forums.
Arena point gain is intentionally different, and this is in-fact not a bug. A typical team will see a small change in their points, but players with very high or very low ratings will see a much larger change. Below is the new formula.
If rating<=1500 then
(note: this calculation can go negative, but will be floored at 0)
If rating>1500 then