order line default price list is replaced incorrectly

We have a default price list set up at the customer account level, and there are many sites under it having its own default price list. When creating an order, the correct default price list is pulled for the header and copied to line correctly per the Defaulting Rule setup. However, when an item is entered at the line, the default price list changes to the one from the account. What's causing this error? Thank you in advance.