The parking brake of Volvo XC90 Mk1 (2002-2014) is weak by design and can not hold the car properly (manual transmission) even if well maintained. This goes back to the small size of brake drums on rear wheels. One needs to keep the 1st gear in to help the engine hold the car when standing still.
Is there some real solution to this problem - maybe replacing the system with Electric Parking Brake? I have not found any reasonable solution online.