...it's happened to me as well. My house was built in '93 and it's happened a few times where it's been extremely cold for a while then there's been a big thaw for a few days. I actually had water running down and coming out from between the window trim moulding and the window frame itself. Quite a bit of it at that.
It's happened at four of the six windows that are immediately below the roof. I'm assuming the water was also running down inside the walls, but I've never seen any water damage looking up from the levels below and there's never been any damage to the ceilings themselves.
This has happened in the area of both a vaulted ceiling and a flat ceiling.
It seems obvious that the moisture in the attic is freezing to the surfaces inside the attic and when the temps rise, it melts and runs down the inside of the roof, dripping off at certain places. Why it doesn't run all the way to the facia boards and drip down and damage the soffits, I don't know.
Better attic ventilation and better sealing between the inside of the house and the attic seem to make the most sense for preventing the problem.