Aged Creditors Report


When I run an Aged Creditors Report I have noticed that the balances per month are not matching. 

For example: I have 1 invoice for October, 2 Invoices for November  for a supplier. When I run the aged report, the report is showing the 1 invoice for October in Period 3 & the 2 November invoices split between period 1 & period 2. Whereas they should both be in period 2. 

My question is am I doing something wrong when running the report?

I need the invoices to be in the correct periods for payments otherwise it becomes messy and suppliers will be short on payments.

Any advice would be greatly appreciated.