That happens to me too near my homestead and other tiles I've previously explored on foot. I think it happens because when you leave a tile, it remembers your previous position, and so if I left on foot before, then the position it remembers is on the shore.
It would be better if it would put me a few tiles away from the save spot, in the water. It's usually not a big deal but if you have a lot of logs on your raft then it can take a long time to get back to the water by pushing everything.