append method breaks final xlsx file

Created originally on Bitbucket by kcaper (Oleksandr Romanets)

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from openpyxl import load_workbook

import os
basedir = '/home/user/projects/test_openpyxl'

template = os.path.join(basedir, 'test.xlsx')
wb_t = load_workbook(template)
wall_sheet = wb_t[u'2.1']
r = [1, 2, 3, 4, 5]

wall_sheet.append(r)

wb_t.save(os.path.join(basedir, 'testfileafterrun.xlsx'))

When updating from version 2.5.12 to 3.0.0 the code above started to break the final Excel file.

In worksheet.py Worksheet.append() the last row of sheet is identified as 1048577, however indicated sheet has only 5 rows.

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Attachments: test.xlsx