Speaking as a parent here, not a tech.
The statement about the seats being all the way back for car seat installations is open to interpretation, IMO. It is included as a "step" in the step-by-step instructions on how to install a car seat in the 2nd row. I personally interpret it as a basic suggestion for convenience, due to the way it is worded and printed. If you look at the other requirements and restrictions that are for safety reasons, the font is bold and/or in larger print, and the statement is VERY clear.
For example, it says DO NOT INSTALL A REAR-FACING CARSEAT IN FRONT OF AN ACTIVE AIRBAG. It doesn't say "When installing a carseat in this vehicle, first place the carseat in one of the rear seating positions, then thread the seat belt through the belt path..." etc.
To me, if the position of the 2nd row seat were a safety issue, it would say "VEHICLE SEAT MUST BE PUSHED ALL THE WAY BACK AND COMPLETELY UPRIGHT FOR CARSEAT INSTALLATION!" It doesn't. It just says "To install a carseat here, push the vehicle seat all the way back, thread the seat belt through the belt path..." etc.
You don't even have to compare it to the wording for something as dire as rear-facing and airbags, though. Compare the wording for the 2nd row seat position and the way they illustrate how to route top-tether straps. Routing the top tether straps correctly is clearly a safety issue, and they address it completely differently in the manual than the vehicle seat position.
Again, that's my personal decision and I what I choose to do for MY family. If someone asked me for my opinion on it at a seat check, when I was speaking as a tech, I'd tell them it appeared to me that the manual was unclear and that they should call Mazda and make their own decision.
One last point - my dd rides in a car seat in the 3rd row, and sometimes the 2nd row seat is all the way back; either because one of her brothers left it that way and they're not with us to fix it this time (and I refuse to stop the car a do it..) or because I'm hauling something that needs the space. She prefers a bit more leg room, of course, but she definitely CAN ride that way. Usually she just crosses her legs.