Yes it is correct behavior. All additions (tip, servicing, etc) and deductions (discount, promotion,etc) spreads to lines so if you use that screen to settle by choosing orders, you can divide total amount properly.
Think it like I ate pizza($12), friend ate burger ($13) we gave $5 tip. Now I want to pay my pizza and friend want to pay his burger.
You can use that setting to see better numbers there.
