+1 My old Trek had a quick release seat post and I had to readjust it once every week or two, depending on how much I rode. On the flip side, a buddy of mine (and his wife) ride Bianchis with suspension seat posts and have used them on a couple of tours without any problem. Just having suspension shouldn't move the seat down the way it sounds like the OP was having problems with, you just might have to set it up a little higher to take the flex into account.