Thank you for your post.
I am able to duplicate the problem. The .xls file works correctly, while the .xlsx appears to evaluate the text string as a number. I have sent this issue to our Development and Software Quality Assurance (Testing) departments for review and confirmation. When I receive more information, I will let you know.
In the mean time, save the file as .xls or export to another format like CSV.
This is one of several times I have sought help on this forum. I have never been disappointed.