This occurs when you're using the Chrome browser, where printing a physical receipt is not an option. After turning the email receipt functionality on, that becomes the only available method of delivering a receipt. This can be fixed by also turning on the No receipt option.
  1. From Tickets, select Sales methods
  2. ​Select Advance sales or Daily Sales (whichever sales method you are using)
  3. Go to the Itemized Receipt Options tab
  4. Select No receipt and click Mark active