I get this error with FMPA17.0.2 on macOS 10.13.6 - haven't tested other configurations.
1. Create a new file in FMPA17 "Test.fmp12" - just a blank file, saving it in a subfolder to the Documents folder - in my case, I call the subfolder "Subfolder".
2. Quit FMPA.
3. Open the URL: fmp://~/Subfolder/Test.fmp12
4. The Window Name and File Name are now "Subfolder/Test", rather than "Test". This affects the information displayed in the login dialogue and window names, as well as the values returned by the Get ( FileName ) and WindowNames functions.