Same file works fine in FMP 12 but broke with an update to FMP 13.
If you are using OS X 10.9 (Mavericks), see if setting your Finder's System Preferences>General to:
Show scroll bars: "Automatically based on mouse or trackpad"
solves this issue.
If this is a windows system, check your Display Control Panel. There's currently a Known Bug with FileMaker displays that affects a number of aspects of what you see on the screen if the Display Control Panel is not set at 100%.
That was the answer.
Thaks to both of you for your feedback.