I seem to be having trouble using keyframes with certain effects. Threshold is one of them. I can add the Threshold effect to a video clip and when I adjust the intensity I see the effect. As soon as I add a keyframe, the intensity setting does nothing. I see the slider moving as I move along the timeline, but I don't see any change to the image. Even if I simply manually adjust the slider (after having placed one or more keyframes), there is no visible effect.
Am I doing something wrong here? I don't have this same problem with, say, the Color Wheel, or things like cropping, with keyframes.