The bug
Slimes and magma cubes do not jump higher with the Jump Boost effect, although it still reduces fall damage for Slimes.
Steps to reproduce
Spawn Slime
Run command
/effect give @e[type=slime] minecraft:jump_boost 60 10 false
Now you should see the particle effect, but the slime doesn't jump higher than normal.
For example see attached video or http://youtu.be/Upb30KUOVCM
Code analysis
Code analysis can be found in this comment.
Linked issues
is duplicated by 3
relates to 4
Attachments
Comments 40
Confirmed
Confirmed for 14w08a and 14w10c

Is this still a concern in the current Minecraft version 14w32d / Launcher version 1.5.2 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.
Tested it in 14w34d. Slimes still don't jump higher with Jump boost effect applied.
Can confirm in 1.18.1.
Can confirm in 1.18.2 and 22w11a.
Can confirm in 1.19.
Can confirm in 1.19.2.

Code analysis (Mojang mappings, 1.19.2): the code for checking the Jump Boost effect is in LivingEntity#jumpFromGround()
, which slimes (and magma cubes) override in their respective classes. In Slime#jumpFromGround()
, instead of
Vec3 $$0 = this.getDeltaMovement();
this.setDeltaMovement($$0.x, this.getJumpPower(), $$0.z);
it should be
Vec3 $$0 = this.getDeltaMovement();
this.setDeltaMovement($$0.x, this.getJumpPower() + this.getJumpBoostPower(), $$0.z);
For magma cubes, it is a bit more complicated, because I am unsure if the jump boost should be scaled with the magma cube's size or not. But it should be an analogous fix.
I really hope this gets fixed, I need it for my map...