Question Reversed animation moves the box more than normal animation

So I have a standard unity cube stretched out into a 10x2x1 'portcullis' for testing. The raising animation seems to work perfectly. However, the lowering animation - literally the same animation with -1 speed - overextends. This means that when you lower the portcullis, it drops too far. Into the terrain. The more you open and shut it, the worse it gets until the gate is impassable. Also, occasionally, the 'go up' animation will send the portcullis on an adventure into the sky for no reason.

Any ideas? My settings for the portcullis are beneath this. It's attached to the gate object, if that makes any difference.