range of data validation changed after setting data

Created originally on Bitbucket by kongyuan (Yuan Kong)

I created a small xlsx file with Excel 2013

yellow cells have data validation which refer to a list [1,2,3] White cells have no validation

here is my code:

#!python

from openpyxl import load_workbook

workbook = load_workbook("test.xlsx")
worksheet = workbook.active
worksheet['A1'] = 1
workbook.save(filename="test.xlsx")

I expect A1 is set to 1, A3 is still blank, and A2 and A4 have no validation drop down.

But the actual is:

You can see A2 now have validation drop down, (which refer to a list [1,2,3])

I tried more and found all cells except last cell (A2, A3, A4, ... Ax-1) was set data validation.

Attachments: test.xlsx