As a Roblox Developer it is currently to hard to apply the Robloxian 1.0 package to R15 players. The only way to do it currently is with a starter character or some other hacky method. We should be able to set the BodyPart properties to 0 or nil in a HumanoidDescription to apply Robloxian 1.0 to R15 players.
By allowing us to do this, it makes avatar editors much easier to make when dealing with bundles / body parts as we won’t have to make an exception to let players use Robloxian 1.0.
Sorry for the late response. The reason for this behaviour is because the rig spawner does not apply bundles for its characters with HumanoidDescriptions, rather it builds with the literal R15 MeshParts for the bundle (these are held internally). Due to this, the HumanoidDescription for generated dummies remains the default object.
You can check out the description for the dummies yourself. If you parent the HumanoidDescription returned from GetAppliedDescription on the Dummy, you’ll see the values for the body parts are zero. This is why the dummy does not get debundled: it does not recognise that there has been a change in the HumanoidDescription, so it skips acting on any values that are still the same.
Now on the other hand, if you make an actual change by giving the dummy a HumanoidDescription, you’ll see that this method does work. To test this, I gave the dummy my own HumanoidDescription while I had a bundle on and then gave it a blank HumanoidDescription. Observe:
Generated dummy → Repro’d your video → Applied my HumanoidDescription to the dummy → Applied a blank, new HumanoidDescription to the dummy
In summary: you need to first have an actual description applied because the dummy generator does not automatically do that, then you can successfully debundle the character by having 0 for the body parts and applying the package. Player characters don’t have this issue since their appearances are now assembled via HumanoidDescriptions.
In summary of the summary: not a bug, what you ran into was the animation plugin not using current standards for applying character appearances.