Oh well, I have no idea why the import would fail.

Anyway, I was able to make a copy of the DB to use in the clean install on another domain. The clean install does work properly with the current database when using "Add selected products to cart" on the product listing page. It also correctly returns to the product listing page.

I'm beginning to think this is an issue with "Display Attributes On Product Listing" mod. Anyone else had issues with that one on V1.5.1?

I'll continue to test and report back my findings.