Last hit bug.

Im playing on a server , i wont give the name but they are having an annoying bug with the last hit on 2 uniques Seth and Haroeris . Seems they cant fix it , so i decided to give a look on here maybe some one has any idea how to solve it .

The bug will go like this : you go inside you can hit as much as you want you will get the kill if you have the most dmg done but there is a chanse you will not the get drop if some one comes and last's hit's the unique , they will get the drop from the box's , anyone know how to fix it ? or did you ever heard of it ?

Regards Tom.