[2021] Voidbringer/Thorn Slinger bug

This is because you are given an extra point skill point to Lunge from Thorn Slinger, which gives +1 to Physical Skills. On default Lunge is a Physical skill. When you take Voidbringer it removes Physical tag from Lunge which then removes the the extra point given to you from Thorn Slinger.

This is intentional.

Thanks for the report.