Error: "Live models can have only one dataset"

[Tim]

I clicked "Duplicate As Live". 

I got an error "Live models can have only one dataset".

I made sure I only have one dataset (see left side of picture below). So why am I getting the error?

I did refresh schema on all tables, and made sure they all point to a view instead of executing a query. 

[Tim]

I opened the .smodel file. Looks like some tables have gone into separate datasets. But in the UI they all list under the same single data source. Is there an easy fix? Or do I have to copy/paste table-by-table within the .smodel file?