Thank you for your post!
Testing and Development is aware of this issue. It seems it can happen as far back as FileMaker Pro 12, though I reproduced the same information you mention. This occurred for me in FileMaker Pro 16, but the navigation buttons were available in FileMaker Pro 15 on both MacOS and the Windows Operating System. I will forward this information to Testing and Development for feedback. When further information is available, I will post back here.