Goatman drops item midair

https://imgur.com/a/ZZ9xlfS

I was using Toxic Rain and I assume the goatman died to DoT damage midair and dropped the Orb of Regret exactly where he died. It is not possible to pick up.
Fortunately it wasn't my first mirror drop.
To me it doesn't seem to have anything to do with skill usage(?) but more the fact that the mob can actually drop stuff outside the constraints of the area.