Trailing interest

monstercop

I am one of the wonderfully lucky Egg customers who has been given marching orders. I recently (last month) changed my payment from minimum payment to full statement balance (never having missed a payment nor gone over the limit!). I paid the full statement balance and have been taken for a 'trailing interest' payment of a minimum amount. Since my DD is set to take the full statement balance I will clear that this month. However, between the statement, and the payment, I have put a sizeable BT onto the card (to remove it soon after - reasons not to go into)which I feel will be stung for trailing interest before it is removed. Is this assumption correct, or have I misunderstood the concept of trailing interest?