Head Restraints
This got my attention, because of Cedric's comment about "active" headrests. That sent me to my manual, and on page 2-16, their function is explained as moving forward in a rear-end impact in order to mitigate head-tilt injury, and whiplash injury. That movement is initiated by the increased body pressure on the seat back, as the impact forces the body rearward from the force of impact.
There is nothing on my '10 (nor any mention in the manual) of any type of device that would cause the headrest to pop upward based on the occupant load. Both my head restraints are locked via a "stop catch release" which engages with an indentation in the head rest tower on one side. (see page 2-15) Once locked it should stay locked. If, however, the restraint is pushed down far enough as to slide beyond the catch point then there may be some condition or another that could cause the restraint to pop upward.
I just went to the garage and took a close look at mine. There are three locking positions on the inside of the left hand post, however only the one that locks the restraint in the top-most position actually locks. It is possible to slide the restraint too far down in the stop catch release to miss the top lock, but it does not matter. Neither the center position, nor the bottom position actually locks. I found any slight pressure does exactly what was reported, allows the head restraint to move up. The bottom position, and the center position notches are not sufficient to stop the head restraint's upward travel once it has begun, and it takes very little pressure to begin the movement.
With all that I can see now that its not the weight of the individual in the seat. but the slight pushing of the head anywhere below the very top of the restraint is what is causing the restraint to move. We're all going to touch the restraint off and on during normal driving.
It seems that the best solution would be to be sure its locked (even though marginally) in the lowest positioning notch - and hope someone from Mazda reads this forum. I am surprised that they haven't seen this as a safety issue and addressed it. I am 6'6" tall, so this isn't an issue with me, it fits perfectly at maximum height (in which it securely locks). However, my wife is 5'6" tall, and now I have to take a look at what I didn't even know was a potential safety problem for her sake.
It's easy to see this restraint moving upward in a rear impact, and not doing its job fully; or making things worse by sliding upward and forcing the head both forward and downward. Kind of like having an air bag only inflating to 50%. May turn out to be nothing, but what is the potential if the restraint slides upward for a shorter driver, and the head impacts the steel upright?
Thanks to ehelp for the awareness.