The bug
I just gave myself a custom splash potion with all positive effects in creative mode and when I splash myself on the head, I seem to fall over a bit in first person mode (hurt animation). However, I am in creative mode and therefore cannot take any damage. But when I put myself in third person mode, I do not turn over. This bug doesn't seem to happen with any other splash potions.
Command to reproduce
/give @p minecraft:splash_potion{CustomPotionEffects:[{Id:10,Amplifier:2,Duration:24000},{Id:21,Amplifier:24,Duration:24000}]}
Expected behavior
The hurt animation would not play because the player is in creative mode and there are no negative effects being applied to the player.
Actual behavior
The hurt animation plays, even though the player is in creative mode and the player is not being affected by any negative effects.
Attachments
Comments 10

Can confirm this behavior in 21w42a. Here are some extra details regarding this problem.
The Bug:
The hurt animation plays when giving yourself the health boost and regeneration effects multiple times through the use of splash potions.
Steps to Reproduce:
Switch into creative mode and give yourself a splash potion that has both the health boost and regeneration effects.
/give @p minecraft:splash_potion{CustomPotionEffects:[{Id:10,Amplifier:2,Duration:60},{Id:21,Amplifier:24,Duration:60}]}
Splash yourself with this potion, wait for a second, and then splash yourself with it again.
Take note as to whether or not the hurt animation plays when giving yourself the health boost and regeneration effects multiple times through the use of splash potions.
Observed Behavior:
The hurt animation plays when giving yourself the health boost and regeneration effects multiple times through the use of splash potions.
Expected Behavior:
The hurt animation would not play when giving yourself the health boost and regeneration effects multiple times through the use of splash potions.