Mine didnt PPK.. I have had this problem before with the specific strain of Italians I got from southern texas.. I say specific strain because its the only Italians I have had, and with the loss of this hive they are all gone, and they all perished the same way.. According to many, WHERE a bee comes from makes no difference.. Hawaii sends bees to Canada and supposedly they do fine there.. I can only speak of the bees I had and the problems with them. My other hives are doing well so far. Hives of Carniolan, New world Carniolan and feral/local bees.. I am going to get a couple of packages from a different southern source and see how they get along.
Sounds like your bees did the same thing mine did, as if the cold was too much for those particular bees to handle.