Nope, but it's probably not "wrong". GPS position has uncertainty, and the altitude is less certain than the horizontal position. Also, when you first have a lock, it's not a a great position lock. You may have noticed this on your iphone or android maps app or Garmin nuvi when you see your position with a big circle around it. That means "I think you're somewhere in this circle, but I don't know where". Same thing applies to altiitude. When you get a satellite lock, you get an altitude number, but as you get a better and better lock, that number will drift towards "correct" (or away from it if you lose a satellite or two). Now, what is "correct". That's a whole other can of worms, because GPS altitude uses a different datum, or model of the world. In short, don't compare baro or other stated altitude sources with GPS altitude and expect 10' precision. Folks that are used to looking at GPS altitude and comparing it to other sources, including "known" altitudes at a particular place in the world, usually recognize that you'll be +/- 0-100' , depending on conditions.
