How so if the net liability change is nil? No extra money comes out of your account, it's just a paper charge that cancels itself. If I have misinterpreted it,

How so if the net liability change is nil? No extra money comes out of your account, it's just a paper charge that cancels itself. If I have misinterpreted it, I would very much like to know so I can inform my accountant. VAT is enough of a hairy mess as it is.