Skeptics.... YOU ARE MAKING THIS WAY MORE DIFFICULT THAN IT NEEDS TO BE!!! IT WORKS PERFECT!!!
When the seat bottom is locked in place, the seat back is locked in place also...
If you were to get into a crash, everything will stay in place due to everything being locked in place.
The only way that ANYTHING moves is to lift up the lever to lift up the seat bottom. That un-locks the seat bottom, and once that is lifted up to about a 45% angle, the seat back raises up enough to unhook the hooks that are holding the seat back in place.
And Yes, you can still lock the seat bottom in the "up" position and the seat back will stay locked in the up position also. Once you are past the 45% angle that I just mentioned, the seat back slides back down into the hook again.
Do this for a test: Lift the handle to UNLOCK your seat bottom.. Once it is UNLOCKED, lift the seat bottom slowly.. You will see that the seat back starts to slide straight up. This is the action that allows you to "unhook" the seat back once the seat bottom is at about 45% angle. Once you have the seat bottom past this 45% angle (and you keep raising it up to lock it in the "up" position") you will see that the seat back starts to slide directly down again- hooking it back in place again.
This is perfectly safe, and nothing moves around when the seat bottom is locked in place.
I've attached a pic of what my seatback "hooks" looked like after I cut them. Don't let the plastic look fool you, there is some pretty thick metal inside the plasic coating, so be sure to start the job with the proper tool- a jigsaw with a metal cutting blade is what I used..