Hi,
Smith Cart version 4.86, Dnn 6.0.2, using the MiniCart module
Steps to reproduce :
Add a product to the cart and clcik 'View cart'
Fill data in the 'Invoice To' fields and click on the 'Confirm' button
Click 'Proceed to checkout' and then 'Back'
ReClick 'Proceed to checkout' and then 'Back'
The 'Invoice To' fields are empty (but the country).