Poser uses spline interpolation by default. That means if say at frame 0 the eyebrow lift is 0 and then at frame 30 you set eyebrow lift to 1 the figure will raise the yebrow from frames 1 to 30.

You either need to specify a different interpolation for that parameter or add a couple other keyframes to control the movement . Use Break Spline for sudden changes of direction.

 

If you select the keyframe in the animation editor and click on the curve you will see a graph that may help you see whats going on.

read the manual for how to set interpolation types, break splines etc.