In a rear wheel drive car, such as the ACVWs, downshifting too early will have the same effect as pulling the handbrake ;-) , especially on a stock engine or an engine with a stock weight flywheel. From the sudden braking, the weight of the car is transfered to the front wheels, and the rear wheels break loose easily. The engine won't have the time to rise the rpms considerably.
Bill, '67 bug.