As I have understood Outlaws previous investigations into payments, there appears to be 2 main software systems that authorities use, one of which allocates all payments to the latest years account, unless specified otherwise. I remember helping someone once, where she was asked to make 2 separate transactions, one for the current years tax and a separate one for the arrears.
In the case of Mag1nMc, the argument is that the greedy council have pocketed the entire payment, leaving the amount outstanding on the original LO as £0. Reg 35(3) of the Enforcement Regs states:
The part referred to is part V1 (enforcement), of which Reg 45 is contained. As I read this, the power under Reg45 has died as the debt and costs associated with obtaining the LO have been settled. The way to have kept the power alive was to divide payments pro-rata.(3) The amount in respect of which a liability order is made is enforceable in accordance with this Part;