"I've actually seen other flags with upside down stars. I believe that it is a fallout from the manufacturing process. The union, including stars, is made as a unit and then sewn into the rest of the flag. Occasionally they get in the wrong way around."
Still, you'd think somebody would have noticed. I like to think I would have, but it took me seven years to notice the upside-down stars on the GOP logo.
US Code Title 4 Section 8(a ) reads “The flag should never be displayed with the union (the stars represent the union of the states) down, except as a signal of dire distress in instances of extreme danger to life or property.”