After Effects added an extra move to the animation, how to get rid of it?
OK, I finally figured it out. This bug is known as "Boomerang Effect".

Reason: Bezier will cause After Effects randomly mass up the path of the shape. 



So you can simply right click the keyframe than select "Keyframe Interpolation" from the menu, than set "Spatial Interpolation" to "Linear" instead of "Auto Bezier", it'll fix everything!

These two video tutorial helped me a lot: AE Boomerang Effect, Part 1 and AE Boomerang Effect, Part 2 they explain the principle of this problem.