First of all, thanks Guyon for the library, it's awesome! You're making a lot of us look good.

The only problem for me is that if I create 2 worksheets with data via

// create the sheets
var leadsheet = workbook.addWorksheet('Leads');
var actionssheet = workbook.addWorksheet('by Actions'); 
// create some dummy data
leadsheet.addRow(['Sheet 1'])
actionssheet.addRow(['Sheet 2'])

I can save the file but when I open it I open up two Excel windows, they appear to be 'grouped'.

To get back to normal you need to close the second excel window, then single select one of sheets, then save. There's got to be an 'active' sheet configuration somewhere although I couldn't see it in code. Any help appreciated.