I have two problems with the shipping parameters

First problem is this: ( I have a formula of 0-680=9+0.19,680-=136+0 ). My Store setting is "Real-time rate calculation and package tracking with United Parcel Service (UPS) or USPS and advanced custom rating system + Specified in Products"

Item A costs 100 with a fixed shipping cost of 25

Item B costs 100 with a weight of 10kg

If you just add Item A the shipping is calculated as 34 total price 134 - incorrect!(should just be 25)

If you just add Item B the shipping is calculated at 10.90 total price 110.90 - correct

When you add both together, it totally ignores Item A shipping and just adds 10.90.

I think I have fixed this by creating this formula 0-1=0+0,1-680=9+0.19,680-=136+0

This seems to work, but only on newly added products, when I add a product that is already in the system, it ignores the fixed cost again!!

My second problem is when I have got two different fixed cost items in the cart

Item Z costs 100 with a fixed shipping cost of 20

Item Y costs 100 with a fixed shipping cost of 25

When you add them individually, it works fine, but when you add them together to the cart it ignores one of the fixed costs so the shipping is 20 or 25 instead of 45!

Can you help please? This is getting quite frustrating!

Andy