When setting up a product and assigning tier pricing and having a product variant with price increase, only the Tier pricing is applied when adding to shopping cart.
Example: Picture Frame: Tier pricing - 2 or more $15, 5 or more $10 Product Variant - Size 8 x 10 (0 increase), Size 11 x 14 ($10 increase)
Selections are displayed for the product detail, but add to cart at a qty of 6 and a selection of 11 x 14 and only the price is reduced for qty and product variant increase is not applied.
Reviewing the PriceHelper.cs I found the following in the "GetUnitPrice" method on about line 273 (version 1.30).
On about line 286 I replaced the Following: if (productVariant.TierPrices.Count > 0) { decimal tierPrice = GetTierPrice(productVariant, shoppingCartItem.Quantity); finalPrice = Math.Min(finalPrice, tierPrice); }
You may just need to search the code for Tierprice and see where it takes you, then walk through the logic to see when and what price is calculated. I haven't looked at 1.4 code yet.