Skimming through it, it doesn't not appear that there is anything prohibiting you from buying the house again. However, you really need to have it reviewed by a local real estate attorney. Logically, if you sold the house in an arm's length transaction and you are buying it in a arm's it should not be a problem.This is the link to the addendum that my wife signed about 9 years ago http://www.care-services.us/forms/fhlmcfnma/FHLMC SS Addendum.pdf.
Assuming the short sale involved a buyer (now the seller) unknown and unrelated to you, and given the passage of nine years, it is probably unlikely that the original lender will be suspicious of your purchase, suspect fraud and seek damages.The seller is the person who bought the house 9 years ago..
You can discuss the addendum and your plans to re-purchase the house with an attorney in your area but, based on what you have said so far, you should be able to buy back the house.Nothing, I used to do telemarketing for the realty that he used to buy this house and number of other houses in this town. I got to know him after a while after visiting our office for other business related activities.
The only risk I see is if the lender sees fraud, even where none exists.If there is no fraud I really see no risk.