Originally Posted by shoerhino

Is there any grease on the seatpost? It might be worth a try to wipe the seatpost clean, just to be sure. Also, is the quick release positioned correctly at the top of the seat tube? It seems very strange that the quick release is that tight and yet the seat post is losing height...

Since the bike is so new, you could have your bike shop take a look for you if there is nothing obvious that you can see.