Credits held on Suppliers Account

Hi I recently raised a question regarding Credits held on Suppliers accounts. When we receive a credit from a supplier I have been holding the credit on the suppliers account. We are given 30 says before the supplier needs paying. The problem I have noticed is at the month end when its time to mark the invoices as paid Quickfile takes this into account to apply credits held on account. This is fine if you only have credits for the month you are dealing with. However if another suppliers credit is raised at the start of a new month it will also present you with this credit too. I only need to apply the credits for the Month I am dealing with at the time. I was assured when I raised it earlier that QF would only present me the supplier credits for the Calendar month I was dealing with but this was not the case. Thanks John