Tweening a welded model with unions doesn't move the entire model

[gameowner101]

I’ve read that in order to tween an entire model, you’re supposed to weld the parts together and then tween the primary part. I’ve done that and it works perfectly fine. The issue arises when I start to use unions, I welded them together using weld constraints, the weld definitely works and whenever I apply any velocity the two unions are stuck together, yet when I tween them only one of the parts seem to move. What is the issue here?
Here’s the script:

local TweenService = game:GetService("TweenService")

local TestParts = game.Workspace.Model
local TestPrimaryPart = TestParts.PrimaryPart
local TweenPositioning = TweenInfo.new(5, Enum.EasingStyle.Linear)
local Goal = {}
Goal.CFrame = game.Workspace.Target.CFrame

local TestTween = TweenService:Create(TestPrimaryPart, TweenPositioning, Goal)
TestTween:Play()

Here’s the tween only moving one part:

Here’s the weld constraint working when I apply velocity:

[Sleazel]

Tweens behave weird on the unanchored models. Try to anchor primary part, at least for the duration of the tween. Do not anchor welded part, as this will break the model.

TestPrimaryPart.Anchored = true
local TestTween = TweenService:Create(TestPrimaryPart, TweenPositioning, Goal)
TestTween:Play()
TestTween.Completed:Wait()
TestPrimaryPart.Anchored = false

This should work. If it doesn’t there might be an issue with the welds themselves.

[gameowner101]

Oh anchoring the primary part fixed it. Thank you very much!