I am having a problem where when I set two position key frames the animation acts as if there is a third frame I never place.

For example, I set a key frame at X position 0 and a key frame at X position 10 five frames later. One would assume that the image would go two units along the X axis every frame, but that's not what happens.

Instead, with just two frames, the image will begin moving across the X axis and then half way through the animation it reverses direction, then a frame or two later continues along it's path.

What is going on? Am I doing something wrong? I've check the other properties for that layer and there are only two key frames in the position field. Easy ease is not turned on and when I delete the frames and animate it again I still have this problem.

Thanks for any tips or tricks!