Strange Motor6d behavior causes C0 to change unpredictably

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#1

I have an automatic rigging system in place for some of my models, which seems to work perfectly when playing animations, however changing the position of the RootPart for some reason causes the RootJoint Motor to go haywire. This doesn’t affect the rest of the Rig, only the Motor6d C0 property of the RootJoint. The expected behavior (as far as I know) is for the C0 of the Motor6d to remain at “0,0,0”, but it changes unpredictably as I try to change the Part0 Position of the motor (The RootPart’s position). The below video display the issue:

(Note I interpolate the RootPart Position, that’s why the RootPart goes back to it’s original position)

The code for the rig script:

function GFX:RigPet(Pet)
	local PetParts = Pet:GetChildren()
	
	if not Pet:FindFirstChild("AnimationController") then
		Instance.new("AnimationController", Pet)
	end
	
	local function CreateJoint(p0, p1, parent, name)
		local Weld = Instance.new("Motor6D") -- I prefer using Motor6D
		Weld.Part0 = p0
		Weld.Part1 = p1
		Weld.Name = name
		if name == "RootJoint" then
--Desperate attempt to get the intended behavior...
			Weld.C0 = CFrame.new(0,0,0)
			Weld.C1= CFrame.new(0,0,0)
		else
			Weld.C0 = p0.CFrame:inverse() * p1.CFrame -- This is object space. Equivalent to Part1.CFrame = Part0.CFrame * Weld.C0 if world space
		end
		Weld.Parent = parent
	end

	for i,instance in pairs(PetParts) do
		if instance.Name == "RootPart" then
			CreateJoint(instance, Pet:FindFirstChild("Body").PrimaryPart, instance, "RootJoint")
		end
		if instance.Name == "Body" then
			if instance:IsA("Model") then
				for i,v in pairs(instance:GetChildren()) do
					if v:IsA("BasePart") and v.Name ~= "Body" then
						CreateJoint(instance.PrimaryPart, v, v, v.Name.."Joint")
					end
				end
			end
		end
		if instance.Name == "BackLLeg" or instance.Name == "BackRLeg" or instance.Name == "FrontLLeg" or instance.Name == "FrontRLeg" then
			if instance:IsA("Model") then
				CreateJoint(Pet.Body.PrimaryPart or Pet.Body, instance.PrimaryPart, instance.PrimaryPart, instance.Name.."Joint")
				for i,v in pairs(instance:GetChildren()) do
					if v:IsA("BasePart") then
						CreateJoint(instance.PrimaryPart, v, v, v.Name.."BodyJoint")
					end
				end
			else
				CreateJoint(Pet.Body.PrimaryPart or Pet.Body, instance, instance, instance.Name.."Joint")
			end
		end
	end
end
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