Unable to enter vehicle if restrained person is in vehicle.

When you, as police, restrain someone and put them in your vehicle, irrelevant of whether it's locked or unlocked, you're then unable to get in it yourself unless you lockpick the vehicle. Can't unlock or lock from the outside. 

Can provide a video if you're unable to replicate it. 

How I override this is: I unlock the vehicle, lock it again, unlock it, open the door, put the person inside, get in the car

Note if you pull them out, they're unrestrained again