I have been seeing that since before the patch. It has become a lot more common after the patch. Even giant-caliber cannons (30mm, 37mm, 75mm on b-25H) often show a small hit sprite (NO fireball!!) or nothing. You see the damage, and you get the kill message, though.
EDIT: A lot more common, but still not all the time, I mean. I do see hit sprites too, but sometimes I know I get hits and kills, and get no fireball for my results.