Question on Split Payment Term

Hello,

I have setup a Payment Term and flagged as split pay term with 3 terms like below:

2%N10 - 2% disc. if paid in 10 days

1%N20 - 1% disc. of paid in 20 days.

0%N30 - no disc.

The terms seems to apply based on calendar date instead of what is entered as Invoice date.  Here is the what I tested.

If I create a voucher today with invoice date as 11/21/2013, no discounts are not applied since its taking calendar month into consideration and not finding any discount.

If I use 11/1/2013 as invoice date, it calculates discount correctly.

I believe the Basis date is always looking at calendar month. Can be changed to look at invoice date instead of calendate date?