Wither not affected by Arrows of Healing

The bug

When I was experimenting with the wither, I tried to use a really strong arrow of healing, but it didn't damage it more than a regular arrow would of. I then tried the same level using a splash potion of healing, and it one-shot it. I also used effects level 1 and 2 for healing and the arrow still did no more damage than a regular arrow, but the splash potion did.

Here is a command for a strong arrow:

/give @p tipped_arrow{CustomPotionColor:16711842,display:{Name:'[{"text":"Arrow of Healing","italic":false}]'},CustomPotionEffects:[{Id:6,Duration:1,Amplifier:124,ShowParticles:0b,ShowIcon:0b}]}

Here is a command for a strong splash potion:

/give @p splash_potion{CustomPotionColor:16711842,display:{Name:'[{"text":"Splash Potion of Healing","italic":false}]'},CustomPotionEffects:[{Id:6,Duration:1,Amplifier:124,ShowParticles:0b,ShowIcon:0b}]}