Discounted Amount not reflected in Total Due

Hi guys, I hope someone can help me please.
I applied a 25 % discount to an invoice and it displayed the correct total, but after I sent the invoice, the invoice did not display the discounted amount in the total due slot, but the full amount!

I tried changing settings at Localisation and everywhere I could find anything related to applying discounts, but it still continues to do this when I send or then save the invoice.
It shows the sub-total, it shows the discount applied and then at the total, once again duisplayes the full sub-total before the discount is applied!
Any help would be immensely appreciated.