The brake should definetly release on its own. One thing to check that is easy to overlook is the shaft going through the housing. (The one the brake arm is attached to). It can get corroded and provide a lot of resistance. If it seems tight, clean up the shaft with a wire wheel or sandpaper and lightly grease it and the part that spreads the shoes apart (flat edge that spreads the brake shoes) before putting things together.
This would also be a good time to double check the thickness of the shoes and make sure they are relatively clean.
I'm not near my bike right now so hopefully someone else can comment if the pictures look correct or not.