VAT with coupons

I have a first order 25% discount coupon on my website, which seems to work correctly.

The first order made with this was as follows:

1 Book (0% VAT) Price before discount £2.99
1 set of Runes (17.5% VAT) Price before discount £15.00
Subtotal £17.99
Shipping £2.20
Discount -£4.50 (correct - 25% of £17.99)

This should give an amount due of £15.69

The invoice (and order) then goes on to show:
VAT 0% £0.00
VAT 17.5 % £1.11

Total £14.57

WHY HAS IT TAKEN THE VAT OFF THE ORDER?
Also, the VAT should be on £15.00 - £3.75(25%)= £11.25, i.e. £1.67. How is the £1.11 calculated?

Any advice would be appreciated.

Ousel:

I have a first order 25% discount coupon on my website, which seems to work correctly.

The first order made with this was as follows:

1 Book (0% VAT) Price before discount £2.99
1 set of Runes (17.5% VAT) Price before discount £15.00
Subtotal £17.99
Shipping £2.20
Discount -£4.50 (correct - 25% of £17.99)

This should give an amount due of £15.69

The invoice (and order) then goes on to show:
VAT 0% £0.00
VAT 17.5 % £1.11

Total £14.57

WHY HAS IT TAKEN THE VAT OFF THE ORDER?
Also, the VAT should be on £15.00 - £3.75(25%)= £11.25, i.e. £1.67. How is the £1.11 calculated?

Any advice would be appreciated.

Have the same problems but we are giving a discount of 36% on a very large amount and it is completley stupid calculation ie -£7000 on a £3000 order, but the total came out just a few hundred pounds short of what it should be.

Searched all the threads going back some years - any chance this might be put right ?