a. you are still provisionally rated and rating points do appear quite eratic as stated.
b. The opponent you beat has a rating considerably lower than yours.
I think this may be why, but I am sure someone can correct me on that.
You are still on provisional rating. This means that you get the mean of all games played, whereby when you win the number used is the opponent's rating plus 400. As your op.rating was 950, and you had a rating of 1435, your rating dropped as the rating-number used was 1350. See the FAQ for a more clear explanation.