This is a story of one weird ettin, and a very bad cave.
So, uh....
Once upon a world, there was a cave of giant cave spiders. I think three adventurers died there, with a sizeable number of drunks. So I decided to take my revenge, and started a fort on top of it, hoping to flood the damn place with the water from the aquifer. That I did, ultimately, but the fort had one problem. Namely, the named Ettin. I was kinda scared when I saw "Carpenter's shop destroyed by ettin" and "wagon destroyed by ettin", I though my dwarves are done for. Nothing of the kind! The ettin just stood there, biding his time next to a meat barrel. I drafted all the dwarves and tried to kill the thing. None of 'em even tried to attack it. So, I went to the unit screen, and saw that the ettin was marked as "Visiting". Named ettin. Visiting. Uh-huh.
So, I thought the ettin might just be friendly, and resumed normal work order. As soon as I set up my carpenter's again, the "visitor" ran up and smashed it, then returned to his guard post near the barrel.
At this point I was too busy to think "make up your mind, willya!", so I decided to just take the ettin out of the equation. By channeling the floor under him. And sealing him with a tower-cap floor.
That fixed the problem, even though the fort later died to an iron man, hunger(*sniff*.. meat barrel), and a very bad freezing bug.
So, how exactly common are "visiting" named semimegabeasts? And friendly to boot? If it wasn't for his habit of destroying buildings, I would have put up with him... The bug in this case is either the friendliness, or the building destroying despite the friendliness.