Create payment terms "at the end of the month"

Hi,

I have a problem in order to create a new term of payment "30 days end of month".

I inserted the new condiction in transaction OBB8; in the section "Payment terms" I inserted " Fixed date" = 31, and "Additional month" = 1. With this customizing I have this problem:

- EXAMPLE 1: if the invoice has baseline data = <b>20</b>.07.2007 the due date will be 31.08.2007 --> correct.

- EXAMPLE 2: if the invoice has baseline data = <b>01</b>.07.2007 the due date will be 31.08.2007 --> incorrect! (my correct due date is 31.07.2007)

Someone know how to solve this problem?

Thanks in advance,

Marco Vismara