the thinkware camera requires two circuits to work in parking mode. the first being an always on supply, or in another words, a direct line to the battery, it also needs an ACC on supply, which is only live when your ignition is on, the camera detects the ignition is turned off with this wire then switches to parking mode allowing the camera to run off the always on supply until that drops below a certain voltage.
You said the camera shows the voltage recorded as being way above 12v, 14v in fact which is a typical voltage for a car that is turned on, to be honest that seems a little high if the car is supposed to be off but anyway.
So when you connected up the always on supply and ACC supply, there is a chance that you have actually connected the always on supply up to a circuit that turns off.
for example, the fuse on for my instrument cluster, if I turn the engine off that circuit remains powered, if I connected up my always on supply to that circuit, after about 30min the camera would turn off, it would turn off because that circuit is controlled by my GEM module (car computer) the car keeps it alive for about 30min to ensure certain things are monitored, after a while that circuit is turned off as well which would kill the camera power, you get in to the car, typically the cars computer will detect the central locking opening up and power up some of the system, so even with the ignition off, you check the power supply to see if its power and it will be, because the car just turned it on.
That make sense?