v1b2: "Ungroup Deep" fails on element with incorrect type

I'm using Inkscape v1.0beta2 (6465177, 2020-02-22) on Windows 10, 64-bit.

I've opened a PDF from PowerPoint 2010 using the internal library (the poppler fork). Whe trying to to run extension Ungroup Deep on the file, I'm getting this crash:

Traceback (most recent call last):
  File "ungroup_deep.py", line 188, in <module>
    UngroupDeep().run()
  File "D:\inkscape\1.0b2_2020-02-22\share\inkscape\extensions\inkex\base.py", line 123, in run
    self.save_raw(self.effect())
  File "ungroup_deep.py", line 181, in effect
    self._deep_ungroup(node)
  File "ungroup_deep.py", line 166, in _deep_ungroup
    self._ungroup(node)
  File "ungroup_deep.py", line 115, in _ungroup
    self._merge_clippath(child, node_clippathurl)
  File "ungroup_deep.py", line 86, in _merge_clippath
    use.add('xlink:href', '#' + child.get("id"))
  File "D:\inkscape\1.0b2_2020-02-22\share\inkscape\extensions\inkex\elements.py", line 209, in add
    self.append(child)
TypeError: Argument 'element' has incorrect type (expected lxml.etree._Element, got str)