Quite simply, the "CustomPotionEffects" does not work in with splash potions (note "splash_potion" is the new ID for splash potions as default potions no longer rely on the "Damage" value to determine both the effect and regular vs splash):
/give @p splash_potion 1 0 {CustomPotionEffects:[{Id:14,Duration:600}]}
/summon ThrownPotion ~ ~1 ~ {Potion:{id:splash_potion,tag:{CustomPotionEffects:[{Id:14,Duration:600}]}}}
In comparison to regular potions, in which the effect is applied correctly:
/give @p potion 1 0 {CustomPotionEffects:[{Id:14,Duration:600}]}
For reference, the following is the new "Potion" format that shifts away from using "Damage" values. This is for default potion effects, not custom ones:
/give @p splash_potion 1 0 {Potion:"minecraft:strength"}
Linked issues
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Comments 14


It is also applied correctly when you use tipped arrows to do it, BTW.

Confirmed.
This is going to break some custom maps.

This bug has been existent in ALL 1.9 versions so far, and yet Mojang has not fixed this yet. Lingering potions also experience the SAME ISSUE. I think that Mojang needs to stop messing around, and fix these major bugs that break peoples custom maps and worlds.

Nick, shouting and complaining will not help. Voting will.
Thanks for reporting!

Hey Mojang, 1 year later with Version 1.9.4, it's still bugged!!!

@@unknown This was created and fixed a year ago. Potions work fine.

Ok go in minecraft 1.9.4 and try to make a splash potion with the color of healing_potion like this:
/summon Item ~ ~1 ~ {Item:{id:splash_potion,Count:1,tag:{CustomPotionEffects:[{Id:23,Amplifier:1,Duration:3600},{Id:22,Amplifier:1,Duration:1200},{Id:6,Amplifier:1,Duration:0}],display:{Name:"Potion Splash de Défense",Lore:["Splash Defensive Potion"]}}}}
Saturation effect d'ont work... And you can't choose the color of your splash potion.

@@unknown You'll notice that your CustomPotionEffects
does work to some extent. This report was about it not working whatsoever. If you have a new issue, create a new report.
And please use the "preview" button before submitting comment. Every single edit you perform is sent to everybody who followed this report.
Confirmed even with a complete tag: