Instead it should make a copy and insert the copy without affecting the attached item.
SVG 1.1 specs: https://www.w3.org/TR/SVG11/types.html#InterfaceSVGLengthList
SVG 2 specs: https://www.w3.org/TR/SVG/types.html#TermListInterface
This will affect the following methods:
of the following interfaces:
This is already fixed by removing the SVG properties tear off objects.
*** This bug has been marked as a duplicate of bug 191237 ***