Coupons can cause totaling errors at checkout!

[danceswiththewolf]

Hello Again!
Just a quick one I've found, I can't explain it and I've bounced the math round my calculator a few times to see what the problem is.
I have a %10 coupon created which seems to work OK and has before , but has caused a problem at check out. I've pasted the details of an order below-

Clearly the maths is wrong and it is not a %10 discount, although it seems to work out the discount itself OK, It just stops the checkout adding things up correctly. VAT is at 15% and I've tried a couple of variations to see if it's having any effect but nothing I can think of gets close to causing the huge discount seen in the final total discount given to the customer.

The total should be
Sub-Total: £227.99
Table Rate (Best Way): £5.87
Discount Coupon: olga10 : -£31.04

Which should add up to £202.82

I have no idea how £157.42 is ending up on the bottom line!!

Any ideas??? Thanks Kenny.

Invoice No. 4457
Date Ordered: Friday 20 November, 2009
Payment Method: Gift Certificate/Coupon
Products Model Tax Price (ex) Price (inc) Total (ex) Total (inc)
3 x Trackmaster Rocky 4914 15% £8.69 £9.99 £26.06 £29.97
1 x Trackmaster Emily 4814 15% £8.69 £9.99 £8.69 £9.99
2 x Trackmaster Molly* - Discontinued 4922 15% £6.52 £7.50 £13.03 £15.00
1 x Trackmaster Neville* - Discontinued 4920 15% £6.52 £7.50 £6.52 £7.50
1 x Trackmaster Bill* - Discontinued 4925 15% £6.95 £7.99 £6.95 £7.99
1 x Trackmaster Douglas* - Discontinued 4924 15% £6.95 £7.99 £6.95 £7.99
1 x Trackmaster Gordon 7443 15% £8.69 £9.99 £8.69 £9.99
2 x Trackmaster James 7444 15% £8.69 £9.99 £17.37 £19.98
1 x Trackmaster Salty 4798 15% £8.69 £9.99 £8.69 £9.99
1 x Take Along Bertie TA76202 15% £3.82 £4.39 £3.82 £4.39
2 x Take Along Jack TA76211 15% £3.82 £4.39 £7.64 £8.78
2 x Take Along Alfie TA76212 15% £3.82 £4.39 £7.64 £8.78
1 x Take Along Max & Monty TA76215 15% £6.25 £7.19 £6.25 £7.19
1 x Trackmaster Percy 7445 15% £8.69 £9.99 £8.69 £9.99
1 x Trackmaster Billy 5723 15% £6.95 £7.99 £6.95 £7.99
2 x Trucks: Farmer McColl's Farm Pack - OUT OF STOCK 5735 15% £8.69 £9.99 £17.37 £19.98
3 x Trackmaster Flora 5724 15% £6.52 £7.50 £19.55 £22.50
2 x Trackmaster Proteus 5726 15% £6.52 £7.50 £13.03 £15.00
1 x Thomas and Friends 4 in a box jigsaw 07297 15% £4.34 £4.99 £4.34 £4.99
Sub-Total: £227.99
Table Rate (Best Way): £5.87
Discount Coupon: olga10 : -£31.04
Total: £157.42

[danceswiththewolf]

Just noticed that it is very close to applying the %10 discount correctly and then adding another %20 on top....( within 3 decimal places)
Strange.