Me and my friend were playin some rebound mode to help him level up while playing I shot a Strobie into the AOE of the black hole and it went in a cicrle and hit the bounder at which point it followed the same path back out of the blackhole and proceded to fall right through the ground and went off screen and suddenly hit my friend. In summary hitting a baounder in a blackhols AOE makes you shot go through the ground off screen and pop up somewhere random or direct hit the enemy. Thats all I know.
I've noticed this bug a number of times, mostly just bounce-type weapons that hit the ground and go through a blachhole's radius tend to phase through the ground then later hit the ground. Though there isnt too much issue in my opinion because in all the cases I've seen - it does hit the ground in the correct spots, not randomly. So it mostly just entertaining, but a bug is a bug and it does need to be fixed, im sure the devs have noticed it since its semi-common and there are plenty of gifs and videos with that kind of stuff happening.