Magento Configurable Product Price Overriding Simple Product Price

Question

I have products set up identically (as far as I can tell) and they were all imported with a universal CSV template.

• Configurable price is 29.99
• Associated Simple Product Short Sleeve is 29.99
• Associated Simple Product Long Sleeve is 39.99

An invoice recently billed a long sleeve product (ZTWS-SBLS-XL) that has a price of 39.99 with the configurable product price of 29.99. How can I force the simple product price to override the configurable product price? Both products below are set up identically with their parent configurable product and as simple products.

Invoice:

Item             Sku             Qty    Subtotal
Item one         ZLOB-SBLS-XL    1      $39.99
Item Two         ZTWS-SBLS-XL    1      $29.99

EDIT: Still working on resolving this. What would cause Magento to prefer the simple product price over the configurable product price or the associated product attribute price?