Joints not readjusting when setting BasePart.Position

[GigsD4X]

In certain builds containing parts connected to others through JointInstances, setting parts’ Position property occasionally leads to other parts being dragged along (as opposed to the expected behavior of the parts’ joints being updated).

Running the following code in the command bar for the attached place file seems to highlight the issue:

local part = workspace["Observation Tower"].Roof.TestPart
part.Position = part.Position + Vector3.new(0, 1, 0)

Position Setter Repro.rbxl (117.4 KB)

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This is assuming the following behavior is what should be expected:

@ContextLost

BasePart property setters will no longer implicitly BreakJoints or MakeJoints . The respective C0/C1 CFrame of any JointInstance joints will be updated to allow the part to move, similar to WeldConstraints .

• BasePart.Position
• BasePart.Rotation
• BasePart.Orientation
• BasePart.Size
• BasePart.Shape
• BasePart.___SurfaceType

Changes to Auto-Joints and Part Properties

[AshCr4ft (AshCraft)]

experiencing this bug too, im trying to tween the orientation of a part with a weld attached onto it

expected result:

actual result:

the top part (unanchored like it should be) is welded onto the bottom; what should happen is the top part should move with the bottom part, however its not doing that

edit: this bug only happens in studio when pressing Run; tween works as expected in-game and in Play Solo however parts do seem misplaced, still moving with the welded part nonetheless

same result happens with a motor6d

[PeZsmistic]

For OP’s case, setting RootPriority of TestPart to be greater than 0 seems to enable the expected behavior.

[GigsD4X]

This seems to be a workaround but is incredibly laggy when working with very large numbers of interconnected parts