Openpyxl load_workbook and save take too long

The following lines take 45 seconds the first, and over a minute and a half the second. Something.xls is 4 MB big and the changes are minor. Is there something wrong?

something = openpyxl.load_workbook('Something.xlsx')
something.save('Something.xlsx')

Some details: I'm using Python 2.7.3 on Windwos 7, the workbook has 2 sheets the first of which has 67610 rows, I'm not accesing any network to do this job.