This type of motor anchor is to keep the rubber motor from climbing over the motor anchor and bunching at the rear of the fuselage. 

Perhaps this photo will help you visualize the wobbly peg. The smaller tube would be the motor peg in your model. The larger tube should be a couple of sizes larger than the peg to allow the unwinding rubber motor freedom to wobble and mover around. This helps the motor to unwind smoothly and evenly.

Thanks to Tarheel on HPA for this info and photo.