Saving this workbook fails

Created originally on Bitbucket by Emery Berger (emery@cs.umass.edu)

Opening this sheet as not read-only and saving it fails reliably. Worked with a previous version.

#!python

import openpyxl

fname = "sheets/subjects_xlsx/01sumdat.xlsx"
outname = "testme.xlsx"

workbook = openpyxl.load_workbook(filename=fname, read_only=False)
workbook.save(outname)

#!python

$ python repro.py 
Traceback (most recent call last):
  File "repro.py", line 7, in <module>
    workbook.save(outname)
  File "/Users/emery/anaconda3/lib/python3.7/site-packages/openpyxl/workbook/workbook.py", line 396, in save
    save_workbook(self, filename)
  File "/Users/emery/anaconda3/lib/python3.7/site-packages/openpyxl/writer/excel.py", line 294, in save_workbook
    writer.save()
  File "/Users/emery/anaconda3/lib/python3.7/site-packages/openpyxl/writer/excel.py", line 276, in save
    self.write_data()
  File "/Users/emery/anaconda3/lib/python3.7/site-packages/openpyxl/writer/excel.py", line 76, in write_data
    self._write_worksheets()
  File "/Users/emery/anaconda3/lib/python3.7/site-packages/openpyxl/writer/excel.py", line 216, in _write_worksheets
    self.write_worksheet(ws)
  File "/Users/emery/anaconda3/lib/python3.7/site-packages/openpyxl/writer/excel.py", line 201, in write_worksheet
    writer.write()
  File "/Users/emery/anaconda3/lib/python3.7/site-packages/openpyxl/worksheet/_writer.py", line 357, in write
    self.write_tail()
  File "/Users/emery/anaconda3/lib/python3.7/site-packages/openpyxl/worksheet/_writer.py", line 345, in write_tail
    self.write_breaks()
  File "/Users/emery/anaconda3/lib/python3.7/site-packages/openpyxl/worksheet/_writer.py", line 241, in write_breaks
    self.xf.send(brk.to_tree())
AttributeError: 'tuple' object has no attribute 'to_tree'

My code (not this piece) is now failing on 16 other spreadsheets it previously worked on, and I suspect the problem is the same.

Attachments: 01sumdat.xlsx