Ok, I was on a little nature walk - since I'm bored (full stomach, no more item tech trees for now, full curiosity page), when I came across a pair of boats. So I lifted one boat, hearth'd, and set it in my temporary base.
So, this was rude, ya - whatever. So I went back to the scene of the non-crime and left a runestone saying I jack'd their boat...
WHILE I WAS CARVING THIS MESSAGE - a boat coasts by, carrying another boat... and sure enough, that was MY boat (as well as the one I stole)
lulz