Thanks for the reply Nicolas,
Two different orders created:
Order 1:
Coupon 5.00, with no rules.
2 Products, one for 150.00+30.00Tax, one for 24.00+4.80Tax.
Shipping 8.40
The value in order_discount_tax = 34.80000
I believe it should be 0.83333
Order 1:
Coupon 6.00, with no rules.
1 Product, for 23.33+4.67Tax
Shipping 7.20
The value in order_discount_tax = 4.67000
I believe it should be 1.00000
Tax is as for UK at 20%
The orders show with correct values at the backend, so the column may not be used there. I was looking at the data in MySQL so that I can access it from another source and saw this as a discrepancy. I have got around this by doing calculations, but thought you may need to know about it.
Let me know if you need more information.