[Python] Unexpected Sheet Renaming in OpenPyXL When Only Case Changes

I'm using OpenPyXL in Python to manipulate Excel workbooks. I encountered an unexpected behavior when renaming a sheet. If I change the name of a sheet to a name that only differs in letter case from its previous name, OpenPyXL appends a '1' to the new name.

Here is a Minimal Reproducible Example:

import openpyxl
# Create a new workbook
wb = openpyxl.Workbook()
# Get the default sheet
sheet = wb.active
# Rename the sheet to 'Input (Raw)'
sheet.title = 'Input (Raw)'
# Rename the sheet to 'Input (raw)'
sheet.title = 'Input (raw)'
# Print the current title of the sheet
print(sheet.title)


Expected Output:

Input (raw)


Actual Output:

Input (raw)1


I'm using Python 3.11.1 and openpyxl 3.1.2.

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