Hi Anson,
I have a SP custom table that was the Product Codes and Descriptions. When you select the drop-down list for the Product Code it then initiates a rule that populates the Description field using the "Set a field's value" by using a "Filre Data" where Product Description (Secondary) (Product Code(secondary) = Product Code (Main)) - obviously in the 'real code' it does not have (Secondary) and (Main), I have just included for explaination.
This seems to work in the repeating table, however, when you 'Insert' more than 4 rows all subsequent Product Descriptions take on the value of the 4th Product Description.