The bug
Effect amplifiers are read/written as byte (-128 to 127) from/to NBT instead of an integer (-2,147,483,648 to 2,147,483,647) which is how it is stored in memory. This causes a change is behavior when the effect is reloaded from NBT is the amplifier is above 127.
How to reproduce
Give yourself jump boost with an amplifier higher than 127 using
/effect/effect give @s jump_boost 100 128Try to jump
→ You cannot jump (see also MC-90198)Reopen the world
→ You now have jump boost with an amplifier of -128 when read (though will be considered 0 when an amplifier obtained via NBT is less than 0)
Code analysis
Based on 1.12 decompiled using MCP 9.40 PRE 1
The methods net.minecraft.potion.PotionEffect.readCustomPotionEffectFromNBT(NBTTagCompound) and net.minecraft.potion.PotionEffect.writeCustomPotionEffectToNBT(NBTTagCompound) reads/writes the amplifier as a byte, while it is stored in-memory as an integer.
Linked issues
is duplicated by 9
MC-108980
jump boost 128 changes it's behavior after relogging
Resolved
MC-112246
Potion levels higher than 127 do not work after relogging
Resolved
MC-165572
Relogging while having an active potion effect will not trigger its effect
Resolved
MC-206105
The jump boost effect does not work when its applied with commands and the particles are hidden
Resolved
MC-208521
Resistance & Regeneration Status Effect
Resolved
relates to 1
Attachments
Comments 17
Affects haste as well, level 128 causes weird issues, haste won't apply unless you are using the correct tool
[media]
How so? It literally causes a changing of behavior of effects on logging out and back in when the amplifier is over 127. While yes, it's an unsupported amplifier, this does make them extremely unreliable to use.
A highly similar issue with enchantment levels was deemed valid and fixed: MC-131290.
@unknown, seeing as you haven't touched this report since May 2022, would it be OK if I became the reporter? I'll keep this updated accordingly.
@unknown please do not spam old issues with feedback. Please send this to the feedback site or discord server.
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gegy
Can confirm for MC 1.12.1. I thought effects with a level over 4 aren't supported though?