"minecraft:movement.jump" is not honored when riding Slimes and Magma Cubes

Verification builds: Release 924386 - 1.5.0.4 BETA
Summary: If I ride a Slime and a Magma Cube they just slide around like they're on a very slippery surface, they don't use their jump movement behavior.

Repro Steps:

1. Download the 'super behavior bug test time' (tm) map from Greg on Slack
2. summon any of the listed mobs
3. tame them with a beetroot
4. ride it around the box

Observed Results:

1. they slide around

Expected Results:

1. they should jump around. jump, jump, jump up, jump up and get down.

Mobs it's bugged on:
slimes, magma cubes