Capturing Freight but not capturing as revenue

Hi, I want to capture freight on my sales order but not capture it as revenue so I'm using a freight charge modifier. In System Parameters I've left 'Inventory Item for Freight' and 'Invoice Freight as Revenue' blank. When I process my order I see my freight charge on the order. What I notice is that the charge is interfacing through to AR with a LINE_TYPE = FREIGHT as expected. When I run Autoinvoice nothing is done with this line or so it appears.

Why is the charge interfaced to AR in the first place when Autoinvoice does nothing with it?