as i know you cant register in auction house more than 5 times. today i registered someone named FLASH stored 12 times.
Never used it before. I guess it adds 10 additional spaces. Just the item has an outdated description. Shenlong and that Flash dude use them often on Tao server, maybe they can confirm the real amount of space it adds.
This is not a bug or a hack. It was a mistake in the Marketplace description. The Special Auction Pass allows you to register up to 20 items at a time.