This is really a bug. It is related to the special points given to submission authors and to authors of a review. Computing points is unfortunately distributed over the whole system and is executed always upon an action resulting in points (for PO only for voting, but the system computes also points for posting). I assume, I have introduced this bug with the changes made to give reps to review authors (100 points per vote), which I have made some weeks ago.It should be fixed now, but I am not yet really sure if it has gone. Please continue to observe your points.
I am very sorry about this inconvenience. I will introduce a more meaningful point accounting index on the user profile page, so that you all are able to understand and check in detail, where your points come from. The original Q2A activity index is not so clear in my opinion. Please give me some time.