It has been noted that printing documents one-sided is not working as you might expect it to and Microsoft Excel produces so really interesting results when the issue occurs. The problem stems from the fact that the printers properties override the application (in this case Excel) properties. Instead of using Excel’s properties to choose one-sided as shown here:
and then choose One-sided and OK in the dialogue that opens, shown here
Notice that when you return to Excel, the printer has changed the Excel print dialogue to say one-sided AND now it will actually print one-sided.