another thing is I think is bug also, almost same situation:
let say
coupon $50
product A: $15
courier fees (belows $300, should have $8 of courier fees): $8
So, the total should be:
* total = $0 + $8 = $8
but system give me total: || $0 + $8 - $50|| = $0
means the coupon calculation also deduct the mininum courier fees, meanwhile the coupon system is
set to not have negative total (Allow negative order total? =false),
and the sort order of coupon is higher than shipment.:
this is the order_total module page sort order:
COUPON 1
sub total 2
shipment 3
Grand total 4
try this sort order also same bug result:
sub total 1
COUPON 2
shipment 3
Grand total 4