Thank you for your post.
I am able to replicate the issue. It appears that FileMaker Pro does not recognize the formatting option within the Excel file. This is evident in the import dialog box as you see the values being imported into the Text field.
I have sent your post along with my findings to our Development and Testing departments for review. When I receive any feedback, I will let you know.
Until this is changed, save the file as a comma-separated values (CSV) text file, and then import the CSV text file into FileMaker Pro.