Setting the CollisionGroupId of a HumanoidRootPart to Non-Existant One Makes It Not Respect Hip Height

As the title says, when a HumanoidRootPart’s CollisionGroupId is set to one that doesn’t exist and never has existed in the current DataModel, it causes it to not respect the HipHeight property of its respective Humanoid.

Here’s a video to demonstrate what I mean:

Disregarding that the HumanoidRootPart appears to zoom off into horizon (that’s a totally different issue), you can see that there’s a very clear difference in behavior between the normal and bugged Humanoids. Attached is a model containing the 4 humanoids in the video:
humanoid-glitch.rbxm (4.2 KB)

To make this happen without the models:

  1. Open a new place to ensure there’s no issue with Collision Groups already being defined
  2. Make a humanoid of either R6 or R15 with any positive non-zero HipHeight
  3. Change the HumanoidRootPart’s CollisionGroupId to 1 instead of 0
  4. Watch as the Humanoid falls to the ground in complete disregard for the HipHeight property

This is easily solved in-studio by opening the Collision Group Editor, creating a group with the same ID, then destroying it. After that, it won’t happen even after a save and reload.