In the screenshot, I just killed a rogue, but the dripping blood animation persists.
At first I thought, it might have to do with the rogue's stealth mode, but it does not.
When I killed the next group of monsters, the same thing happened. Notably, the dripping blood animation is at the place where my own character was standing when battling 3 monsters.
Going back to the place from the screenshot, the persistant animation there had gone away. So it seems, there will only be one persistant animation at a time, getting another one will cause the previous one to disappear.
If the persistant animation isn't replaced by another one, it seems to stay indefinitly. I did not try exiting and coming back to the level, but wandering around, resting out of sight, and coming back to the spot, the animation is still there.
EDIT: oops, perhaps this is in the wrong bug forum. I hope it gets noticed here