I have the opposite problem -- we have the Tips option turned off in Settings, and it doesn't show up when we create and save an invoice, but then when we re-open (or the customer opens) the invoice, the TIP line suddenly shows up. 

We don't want the Tip line showing on invoices. 

I've contacted QB Support multiple times, but so far no one has been able to get rid of the unwanted Tip line on invoices. 

So be sure that you want it if you enable that feature -- you might not be able to get rid of it.