If the door is balanced with the opener disconnected, meaning that it will stay put when it is around half way open, then the spring is properly wound. If the spring is under wound the door won't balance and the cables will go slack and fall off the drums as the spring stops turning before the door completes its travel. Over wound the door will runaway as it approaches fully open, and if over wound enough may drift open on its own or dangerously out travel the length of the horizontal track. A torsion spring exerts a varied effort on the door as it moves to support only the weight that is in the vertical section of track. With the door closed the spring is under full tension, then for each foot of travel as the door opens the drums make one full turn (and therefore so does the spring) reducing the amount of energy stored in the spring and the amount of weight it will carry. The extra 1/8 to 1/4 turn is there to maintain some tension on the cables when the door is in the fully open position so that they rewind properly as the door closes. Wooden doors complicate the spring calcs because they are never a consistent weight from one door to the next, and that weight changes as frequently as the weather. The down and dirty fix for that door is to bolt on a piece of perforated angle that is at least 50% longer than the distance between the vertical stiles, preferably as long as the door. The proper fix is to have a new panel fabricated and installed with a steel strut across the top rail. In either event the opener needs some serious adjustment. A properly adjusted opener just doesn't generate the force to pop a finger joint like that, even if the seller closed it on her car (an educated guess).