Shipping address keeps reverting to billing address

For some reason, when a customer enters a new address in their address book, and then selects this as the shipping address, when they come to the final screen before payment, it has reverted back to the billing address as their shipping address. I even tried making the new address the primary address, and it still reverted back to the billing address. So, currently customers cannot use an alternate shipping address.

I am using ZenCart 1.3.8a. You can try it out at this site: https://www.simplycheese.net/store. I'm not sure where to look to fix this. Any help would be greatly appreciated.

:frusty: Does no one have an idea on this one? I'm still having the problems, and it is a pain since customers want to send Xmas gifts to family and friends. Can anyone give me a hint where I might look to solve this issue?

I'm running 1.3.8a. Thanks!

Regretfully, I still have a copy of v1.3.8a kicking around. I just did a fresh install of it, and tried to recreate what you're talking about. I can't.
This suggests that something's wrong with whatever you've done/added to customize your site ... either addons or custom code, or some peculiar combination of admin settings I've not seen before.

To fix your problem, it first must be recreatable on a new clean site.
So, prepare a list of everything I need to do to my fresh clean install to make it operate exactly like yours does.

I installed the mod "Fast and Easy Checkout" and this seems to have broken this feature -- plus that mod never worked; I'd stay away from it. I tried to uninstall FEC, but that broke my cart altogether, so I reinstalled it and the alternate shipping address seems to be the only thing broken as of now. Any ideas?:(