Anomaly Review Board (ARB) Final Presentation available here.
Since early 2004, the difference between HST's uncompensated gyro drift rate bias and the on-board commanded bias correction has been increasing. This effect appears during HST's night/day transition and is only observed in the V2 axis.
Telescopes Branch members are involved in the Attitude Observer Anomaly Working Group and the Anomaly Review Board, investigating this issue and making recommendations, respectively.
AOA Working Group's website
Anomaly Review Board's website