This happens in Operation Avalanche in BTR-
Two days after the allies invade the toe of Italy, I sent all 4 B-25 groups together against Foggia railyard. In an open (?!) area southeast of Naples, far from any target but near where the front line would be (actually probably on the allied side), I start taking flak hits. A LOT of flak hits. What the heck? Turns out, the flak slaughters the formation. I lose 50-60 B-25s, or about half of the force! I would accept it, if I overflew a defended target, but I was careful to keep my waypoints away from anything major.
Is this a bug, or some kind of feature? Do the defenders have a way to build up a huge hidden flak trap? I've played as the Germans, and I am unaware of any way to do this. Does it represent friendly fire? Or an abstract Vesuvius eruption? I have the saved scenario that causes this, if anyone is interested.