Chart sheet keeps getting removed when editing a file
Hi there, I'm running into an issue which can be reproduced with this attached file: [buggy.xlsm](/uploads/43c98686abe69e692208e78d497ca0d3/buggy.xlsm)
I'm not even editing the file, all I do is load and save as such:
```
wb = load_workbook('buggy.xlsm', keep_vba=True)
wb.save('INTERNAL_TEST.xlsm')
```
And when I open the new file, I first get an error about the file being locked:

And then when I bypass, I get another alert saying that my chart sheet was removed:

Any idea why this is going on?
Thanks!
issue