Park brakes aren't always that successful - the A109 early series used the hydraulic pressure (with engine/s running) which was stored behind a valve for parking when you pull out the park brake handle and press the brakes. Sadly, after shutdown the stored pressure would bleed away, and if the bird wasn't chocked, it might just roll off downhill.
Yes, they didn't change the design on later marks, either. It's caught many a pilot out (me included). If you're single pilot and the aircraft is leaning on the chock because sufficient brake pressure isn't available, you need to start up to re-pressurise the utility hydraulics, re-apply the parking brakes, shut down, remove the chocks, start up again and taxi away.
The other "gotcha" on that aircraft is that the rotor brake pressure works in a similar way. Woe betide the pilot who starts his 109 with the rotor brake "on". If the pressure has bled away, the rotors will start turning as per normal - until the hydraulics re-pressurise, whereupon the rotor brake will re-apply itself. One pilot I know started his first A109 job in the morning, burned out the rotor brake, damaged the transmission and was out of a job early afternoon.
Almost as silly a design as the SK76 where the aircraft can't be safely towed unless undercarriage locking pins are inserted.