Tactics Trainer Rating Calculation

Has the algorithm for calculating the rating in the Tactics Trainer changed?  It seems now if I drop below my rating by 100 points or so, each additional mistake is severely punished (-20) and any correct responses are only slightly rewarded (+3).  The next day, the Tactics Trainer seems to reset its baseline to my new, lower rating.  I never remember it being this way until recently.  It is most discouraging.

you probably responding slow to the problems at hand, when I solve problems at good time I gain 9-13 points per problem

I just recently solved a problem with 75% of the time remaining and only received two points.  This implies if I had solved the problem with 100% of the time, I would have only got three points.  I do believe something is amiss.  I have also been getting many of the same problems back to back.