Brigala
CPST Instructor
I think it should lock into place. Does it have the notches on the side on one post? It should click in at each one. I stored headrest for any car I have had in the back of the car and have had no issues. We have had like 5 Mercedes SUVs over the years and a bunch of minivans. We have packed luggage on top etc... And they have been fine. We have also gotten them dirty whatever was in the trunk and they wipe up fine.
It does have notches. When going UP, it slides freely. All of them do, in all the positions, and that's what's also indicated in the manual, so I'm sure it's not a malfunction.
To push it DOWN, you have to push the release button.
I actually like this because it makes it much easier to reach behind your own head and move the head rest up instead of doing contortions in the car to get it in the right place.