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Check your motion path. Odds are the bezier handles are pulled out in the direction of the motion. The quickest fix for this is to change the spatial interpolation of your keyframes to linear.
This rebound effect is caused by Bezier interpolation of the temporal keyframes. You can actually see this in the Composition Window if you've elected to display keyframes in the preferences and you have position keyframes selected in the timeline.
The easiest fix is to simply select the keyframe that is giving you the problem in the Comp window, then hold down the G key. Your cursor will change to something that looks like > when you hover over the keyframe. When you click on the keyframe the interpolation changes from Bezier to Linear and solves the problem.
You could also select the Bezier handle and drag it around to fix the problem.
The last option works in the Timeline Window. You select the errant keyframe (or all of them if you want to change interpolation of all the keyframes for that property) then you right click or Control + click on a Mac on the keyframe and select Keyframe Interpolation. You change the temporal interpolation to linear and you're done. This is exactly the same thing as clicking on the keyframe in the Composition window with the G key held down.
If you have problems with animation paths, like Anchor Point, that do not show up in the Composition window then you can open that layer in the Layer window and select the appropriate property from the pull down menu on the right.
I hope this helps. Seems like I just answered this question a few hours ago.
Some people call this "boomerang" motion.
Here's an After Effects Community Help search for 'boomerang' that brings up a few pages that explain the issue. One of the Community Help search results is for a video by Aharon Rabinowitz that does an especially good job of showing what's going on.
Here's an excerpt from the "Controlling change with interpolation" section of After Effects Help on the Web that summarizes the issue:
"Note: In some cases, the Auto Bezier spatial interpolation for Position keyframes can cause undesired back-and-forth (boomerang) motion between two keyframes with equal values. In such a case, you can change the earlier keyframe to use Hold interpolation or change both keyframes to use Linear interpolation."
OK, got it. Many thanks!