this problem is somehow tied to attributes

when i do a live test with a product set up for just a download and the download/model sku associated to ANY the transaction completes ok and i am returned to the completed page

when i associate the file download to a attribute and choose that at the product/features/download/model sku (File Download) i am returned to the cart page

both instances show file in accnt file download area and both get email notifications

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i tried again and the 1st time it worked with just a standard download and i am returned to the completed page

tried attribute download and i was returned to cart

tried one more time on standard sku(ANY)download, no attribute, and was returned to the cart page