This is from an old NYT article and what I find interesting is the last sentence.
"The current S.E.C. rule applies only to stocks traded on the New York Stock Exchange and other exchanges -- not to stocks traded on the Nasdaq. It says a short sale may be made only at a price higher than the last different price. The Nasdaq has its own rule, but it relates to bid prices, not to last sale prices. And it exempts market makers."
A case of the fox guarding the hen house.
I like the exemptions you find in the capital markets. Like congressmen being able to trade on inside information until recently where it took two laws, not one, for the lawmakers to comply. And as it applies to Affy the fact that market makers and exchanges can still trade opening contracts in the options market.