Not only jabos drop bombs when attacked. I play a QMB mission now to practice shooting (Crimea, low altitude, my advantage, 4 Il-2m3s + 3 Il-2s 3rd series and me in a Bf 109G-6) and every time I am next to the Ilyushins, they dump their bombs. IMO, they should do it when they're badly shot, unless they are already flying coffins (my attacks usually end up with a tailless Il-2 spinning to the ground after a single very short burst from a 20-50m distance, just like the experts hunted
). So it isn't just fighters' case, it's a common problem, especially in the eastern front.