Coupons are applied Before Promotions

Summary

Coupons are applied before other promotions, which may results (in our case) in some miscalculation of final price.

Expected

We have for instance a product which costs '90' (currency doesn't matter)

We have a first promotion (with no coupon)
- make it 10 minus (price is now 80)

Another promotion with a coupon
- take off 50% (price is now 40)

And a final coupon (for specials customers)
- take 25% more (price is now 30 which is good)

What really happens

Initial price is 90

Coupons first so :

- take off 50% (price is now 45)
- take 25% more (price is now 33,75)

And finaly others promotions

- make it 10 minus (price is now 23,75 which is bad)

My solution

I made a patch which load all promotions, and sort them by weight (defined in admin panel) before apply them on the order.