my almost 13 month old went through the same thing when he was about 11 months, he would stand on his head and look between his legs all the time, and he still does it every once in a while.
my husbands great great grandmother used to say that when a baby does that, it means another one is on the way. thank God that is just an old wives tale or we would have hundreds.
i think it is pretty normal, i also have a 4 year old that done the same thing when he was that age. i think it is just something new and fun to do, and they have found a way to look at things from a new angle.