For some unknown reason, the blades started tracking OK. Flew them 3 times at night without doing any aerobatics. Started feeling very comfortable. So, on the fourth flight went to idle up and let it rip. Did some loops, rolls, tumbles, etc. Then the tracking went out again. So, I landed and will now investigate. I don't think it is the blades now. I measured everything I know to measure and they are fine. It must be something else.

The dampers are at least a year old. N1pster may have it right. I will replace them and see what happens. These night blades are much lighter than the blades I was flying. Would stiffer dampers be the way to go?