The rear armrest in the center of the rear seatback can be used (no occupant in the center seat) or placed upright.

WARNING
Never put your hands and fingers around the moving parts of the seat and armrest:
Putting your hands and fingers around the moving parts of the seat and armrest is dangerous as they could get injured.
Split Folding
Head RestraintsMazda 6 Owners Manual: Contact Authorized Mazda Dealer and Have Vehicle Inspected
If any of the following warning lights or the indicator light turns on/flashes,
the system may have a malfunction. Contact an Authorized Mazda Dealer to have your
vehicle inspected.
...
Mazda 6 Owners Manual: Rear drain hose installation
Caution
If the rear drain hose is pinched or bent anywhere, the water in the hose may
not discharge and enter the inside of the vehicle. During and after installation
of the trims and the headliner, always make sure there is no interference with
the rear drain hose. Fix any problem if foun ...