I have no idea why this happens, but it doesn't exist in FileMaker Pro 14, only in FileMaker 15.
FileMaker Advanced 126.96.36.199
The file has been in existence since several previous versions.
The attached screen shots illustrate the line spacing when "Condensed" is removed from the field properties and it is returned to "Plain Text", and what it looks like when Condensed is chosen. You can see the difference by viewing the Text baselines.