[FP] Unexpected vertical movement when stepping up onto a slab while in scaffolding

Troubleshooting Information

[x] Matrix and ProtocolLib are up-to-date
[X] Matrix is running on a 1.8, 1.12, 1.13, 1.14, 1.15, or 1.16 server
[X] The issue happens on default config.yml and checks.yml
[X] I've tested if the issue happens on default config

Issue Information

Server Version git-Paper-779 (MC: 1.16.5) (Implementing API version 1.16.5-R0.1-SNAPSHOT)

Verbose Messages Move (move.vert) | unexpected vertical movement (motion: 0.5/-0.078, hor: 0.152, buffer: 0.289/true, ground: ++, setback: +, vel: none, from: 63.0, past: 0.0, tags: jump,step,scaffold,high_jump) | vl:15+5 client:1.16.x ping:21 lp:2 tps:20.0

How/When Does It Happen: When you step up onto a half slab from inside of a scaffolding block.

Video:

https://user-images.githubusercontent.com/62695023/124368410-bb261500-dc58-11eb-88fa-9031fb1661a7.mp4

Other Information:

I know the video is on 1.17. I've also tested it on 1.16 and it has the same issue.
The reason the video is in awful quality is because GitHub has a max upload of 10MB and I can't be asked to upload the full quality version to YouTube.

Configuration Files

Link to checks.yml file: Default

re-ovo / Matrix-Issues