/damage returns a fail message and value when successfully damaging Armor Stand

The bug

The /damage command sometimes returns a fail message when successfully damaging target. For example, damaging an armor stand.

How to reproduce:

For example:

• summon an armor stand:
  • /summon armor_stand
• damage it with out_of_world:
  • /damage @e[type=armor_stand,limit=1] 20 out_of_world
• The armor stand is killed, but returns a fail messgae