[Python] python-pptx duplicate slide PPT will be damaged

I found that when using the method of duplicate slide, if there is a chart on the page, PPT will be damaged, so I used this method to copy a slide with a chart and modify the title of the chart on one page, and the title of the chart on the other page is also modified inexplicably

def duplicate_slide(pres,index):

template = pres.slides[index]
blank_slide_layout = pres.slide_layouts[index]
copied_slide = pres.slides.add_slide(blank_slide_layout)

for shp in template.shapes:
el = shp.element
newel = copy.deepcopy(el)
copied_slide.shapes._spTree.insert_element_before(newel, 'p:extLst')

for _, value in six.iteritems(template.part.rels):
# Make sure we don't copy a notesSlide relation as that won't exist
if "notesSlide" not in value.reltype:
copied_slide.part.rels.add_relationship(
value.reltype, value._target, value.rId
)

return copied_slide

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